2006 Nissan Frontier Problems: Fuel system (611 Complaints)

The most-reported problem on the 2006 Nissan Frontier is Fuel system (38% of 611 owner reports). There are 7 safety recalls. Check the VIN and inspect Fuel system — this is the NHTSA file, not a score.

NHTSA Office of Defects Investigation Snapshot 2026-09-07 611 complaints · 7 recalls

What problems show up on the 2006 Nissan Frontier?

230 of 611 filings named Fuel system (38% of the file). That is what owners wrote, not a shop diagnosis of the vehicle in the driveway.

Second is Transmission / driveline (152 reports).

There are 7 official safety recalls on this year. They were filed about Fuel system, Airbags, and Suspension. Check the VIN at nhtsa.gov — a campaign on this page can still be open on a specific truck.

The 2005 has 528 reports on file; this year has 611. Older years collect more reports just by being on the road longer. If you need a fairer comparison, use the equal-time view.

What to check before you buy a 2006 Nissan Frontier

A useful visit to this page takes five minutes. YearTell does not score years and cannot see the vehicle in front of you.

  1. Look up the VIN for open recalls at nhtsa.gov. This year has 7 campaigns on file below.
  2. Fuel system. Check for fuel smell, leaks and whether it starts and idles cleanly.
  3. Transmission / driveline. Have a shop drive it and check the transmission: hard or delayed shifts, burnt-smelling fluid, and 4WD engagement if equipped.
  4. Engine. Have a shop check for oil consumption, coolant leaks, rough idle and unusual engine noise.
  5. Skim a few owner reports below for Fuel system. Look for the same symptom repeating.
  6. Take that list to a mechanic. Do not turn the complaint total into a score.

What owners reported

System named most often: Fuel system 230 complaints · 37.6% of the file
Crashes, fires, injuries and deaths in those filings:
  • Crashes 13
  • Fires 2
  • Injuries 13
  • Deaths 1
NHTSA Consumer Complaints Snapshot 2026-09-07 Open source record Read our complete data methodology →

Complaint counts reflect self-selected reports and are not normalised for production sales volume. We publish no reliability scores, superlatives, or vehicle rankings.

Which systems owners named

Share of owner complaints filed against each vehicle system. These shares are not adjusted for how many vehicles were sold.

Which systems owners named Fuel system (FUEL SYSTEM) appears in 230 of 611 owner complaints (37.6%) in this vehicle snapshot. Fuel system (FUEL SYSTEM): 230 complaints, 37.6% of reports Fuel system (FUEL SYSTEM) 230 · 37.6% Transmission / driveline (POWER TRAIN): 152 complaints, 24.9% of reports Transmission / driveline (POWER TRAIN) 152 · 24.9% Engine (ENGINE): 89 complaints, 14.6% of reports Engine (ENGINE) 2 crash reports 1 fire reports 89 · 14.6% Steering (STEERING): 29 complaints, 4.8% of reports Steering (STEERING) 1 crash reports 29 · 4.8% Electrical (ELECTRICAL SYSTEM): 17 complaints, 2.8% of reports Electrical (ELECTRICAL SYSTEM) 1 fire reports 17 · 2.8% Airbags (AIR BAGS): 16 complaints, 2.6% of reports Airbags (AIR BAGS) 2 crash reports 16 · 2.6% Brakes (SERVICE BRAKES): 16 complaints, 2.6% of reports Brakes (SERVICE BRAKES) 3 crash reports 16 · 2.6% Cruise / speed control (VEHICLE SPEED CONTROL): 9 complaints, 1.5% of reports Cruise / speed control (VEHICLE SPEED CONTROL) 1 crash reports 9 · 1.5% Seat belts (SEAT BELTS): 8 complaints, 1.3% of reports Seat belts (SEAT BELTS) 2 crash reports 8 · 1.3% Unclassified NHTSA leftover: 268 complaints, 43.9% of reports Unclassified NHTSA leftover 7 crash reports 268 · 43.9% 0% 25% 50% 75% 100%

“Unclassified NHTSA leftover” is not a car part. It is a filing bucket and always sits last.

View component data as a table
System / Component Complaints Share of Reports Safety Reports (Crashes / Fires)
Fuel system (FUEL SYSTEM) 230 37.6% 0 crashes · 0 fires
Transmission / driveline (POWER TRAIN) 152 24.9% 0 crashes · 0 fires
Engine (ENGINE) 89 14.6% 2 crashes · 1 fires
Steering (STEERING) 29 4.8% 1 crashes · 0 fires
Electrical (ELECTRICAL SYSTEM) 17 2.8% 0 crashes · 1 fires
Airbags (AIR BAGS) 16 2.6% 2 crashes · 0 fires
Brakes (SERVICE BRAKES) 16 2.6% 3 crashes · 0 fires
Cruise / speed control (VEHICLE SPEED CONTROL) 9 1.5% 1 crashes · 0 fires
Seat belts (SEAT BELTS) 8 1.3% 2 crashes · 0 fires
Unclassified NHTSA leftover 268 43.9% 7 crashes · 0 fires
NHTSA Consumer Complaints, NHTSA Safety Recalls, and NHTSA Defect Investigations Snapshot 2026-09-07 Open source record

Complaint counts reflect self-selected reports and are not normalised for production sales volume. We publish no reliability scores, superlatives, or vehicle rankings.

When reports and recalls showed up

When owners filed reports, and when recall campaigns showed up.

When reports and recalls showed up Owner reports in this snapshot begin in Jan 2006; the first recall shown was reported in Mar 2006. 2006-Q1: 1 owner reports 1 2006-Q2: 3 owner reports 3 2006-Q3: 3 owner reports 3 2006-Q4: 2 owner reports 2 2007-Q1: 1 owner reports 1 2007-Q2: 1 owner reports 1 2007-Q4: 3 owner reports 3 2008-Q1: 1 owner reports 1 2008-Q2: 4 owner reports 4 2008-Q3: 5 owner reports 5 2008-Q4: 11 owner reports 11 2009-Q1: 13 owner reports 13 2009-Q2: 10 owner reports 10 2009-Q3: 12 owner reports 12 2009-Q4: 9 owner reports 9 2010-Q1: 28 owner reports 28 2010-Q2: 42 owner reports 42 2010-Q3: 34 owner reports 34 2010-Q4: 14 owner reports 14 2011-Q1: 22 owner reports 22 2011-Q2: 8 owner reports 8 2011-Q3: 11 owner reports 11 2011-Q4: 12 owner reports 12 2012-Q1: 13 owner reports 13 2012-Q2: 11 owner reports 11 2012-Q3: 18 owner reports 18 2012-Q4: 14 owner reports 14 2013-Q1: 20 owner reports 20 2013-Q2: 18 owner reports 18 2013-Q3: 15 owner reports 15 2013-Q4: 13 owner reports 13 2014-Q1: 20 owner reports 20 2014-Q2: 10 owner reports 10 2014-Q3: 11 owner reports 11 2014-Q4: 10 owner reports 10 2015-Q1: 6 owner reports 6 2015-Q2: 9 owner reports 9 2015-Q3: 13 owner reports 13 2015-Q4: 14 owner reports 14 2016-Q1: 13 owner reports 13 2016-Q2: 14 owner reports 14 2016-Q3: 4 owner reports 4 2016-Q4: 10 owner reports 10 2017-Q1: 3 owner reports 3 2017-Q2: 5 owner reports 5 2017-Q3: 4 owner reports 4 2017-Q4: 5 owner reports 5 2018-Q1: 6 owner reports 6 2018-Q2: 8 owner reports 8 2018-Q3: 7 owner reports 7 2018-Q4: 7 owner reports 7 2019-Q1: 7 owner reports 7 2019-Q2: 6 owner reports 6 2019-Q3: 7 owner reports 7 2019-Q4: 6 owner reports 6 2020-Q1: 5 owner reports 5 2020-Q2: 2 owner reports 2 2020-Q3: 4 owner reports 4 2020-Q4: 1 owner reports 1 2021-Q1: 4 owner reports 4 2021-Q3: 1 owner reports 1 2021-Q4: 2 owner reports 2 2022-Q1: 2 owner reports 2 2022-Q2: 2 owner reports 2 2022-Q3: 1 owner reports 1 2023-Q1: 1 owner reports 1 2023-Q2: 1 owner reports 1 2023-Q3: 1 owner reports 1 2023-Q4: 1 owner reports 1 2024-Q1: 3 owner reports 3 2026-Q1: 1 owner reports 1 2026-Q2: 2 owner reports 2 Owner reports Jan 2006 Apr 2026 Recall campaign 06V092000 ◆ Recall campaign 06V092000 Recall campaign 06E064000 ◆ Recall campaign 06E064000 Recall campaign 07E046000 ◆ Recall campaign 07E046000 Recall campaign 08V690000 ◆ Recall campaign 08V690000 Recall campaign 10V075000 ◆ Recall campaign 10V075000 Recall campaign 10E019000 ◆ Recall campaign 10E019000 Recall campaign 10V517000 ◆ Recall campaign 10V517000 Investigation DP12004 ● Investigation DP12004 Investigation DP26003 ● Investigation DP26003
  • Campaign 08V690000 was reported 864 days after the first earlier complaint mapped to its component.
  • Campaign 10V075000 was reported 621 days after the first earlier complaint mapped to its component.
  • Campaign 10E019000 was reported 29 days after the first earlier complaint mapped to its component.
View timeline records as a table
Date Record type Count Record identifier
2006-Q1 Owner reports 1
2006-Q2 Owner reports 3
2006-Q3 Owner reports 3
2006-Q4 Owner reports 2
2007-Q1 Owner reports 1
2007-Q2 Owner reports 1
2007-Q4 Owner reports 3
2008-Q1 Owner reports 1
2008-Q2 Owner reports 4
2008-Q3 Owner reports 5
2008-Q4 Owner reports 11
2009-Q1 Owner reports 13
2009-Q2 Owner reports 10
2009-Q3 Owner reports 12
2009-Q4 Owner reports 9
2010-Q1 Owner reports 28
2010-Q2 Owner reports 42
2010-Q3 Owner reports 34
2010-Q4 Owner reports 14
2011-Q1 Owner reports 22
2011-Q2 Owner reports 8
2011-Q3 Owner reports 11
2011-Q4 Owner reports 12
2012-Q1 Owner reports 13
2012-Q2 Owner reports 11
2012-Q3 Owner reports 18
2012-Q4 Owner reports 14
2013-Q1 Owner reports 20
2013-Q2 Owner reports 18
2013-Q3 Owner reports 15
2013-Q4 Owner reports 13
2014-Q1 Owner reports 20
2014-Q2 Owner reports 10
2014-Q3 Owner reports 11
2014-Q4 Owner reports 10
2015-Q1 Owner reports 6
2015-Q2 Owner reports 9
2015-Q3 Owner reports 13
2015-Q4 Owner reports 14
2016-Q1 Owner reports 13
2016-Q2 Owner reports 14
2016-Q3 Owner reports 4
2016-Q4 Owner reports 10
2017-Q1 Owner reports 3
2017-Q2 Owner reports 5
2017-Q3 Owner reports 4
2017-Q4 Owner reports 5
2018-Q1 Owner reports 6
2018-Q2 Owner reports 8
2018-Q3 Owner reports 7
2018-Q4 Owner reports 7
2019-Q1 Owner reports 7
2019-Q2 Owner reports 6
2019-Q3 Owner reports 7
2019-Q4 Owner reports 6
2020-Q1 Owner reports 5
2020-Q2 Owner reports 2
2020-Q3 Owner reports 4
2020-Q4 Owner reports 1
2021-Q1 Owner reports 4
2021-Q3 Owner reports 1
2021-Q4 Owner reports 2
2022-Q1 Owner reports 2
2022-Q2 Owner reports 2
2022-Q3 Owner reports 1
2023-Q1 Owner reports 1
2023-Q2 Owner reports 1
2023-Q3 Owner reports 1
2023-Q4 Owner reports 1
2024-Q1 Owner reports 3
2026-Q1 Owner reports 1
2026-Q2 Owner reports 2
Recall campaign 1 06V092000
Recall campaign 1 06E064000
Recall campaign 1 07E046000
Recall campaign 1 08V690000
Recall campaign 1 10V075000
Recall campaign 1 10E019000
Recall campaign 1 10V517000
Defect investigation 1 DP12004
Defect investigation 1 DP26003
NHTSA Safety Recalls Snapshot 2026-09-06 Open source record

Safety Recalls (7)

Official campaigns. Each one says what could go wrong and what the dealer was told to fix.

In short, these campaigns were filed about Fuel system, Airbags, and Suspension.

  1. Recall campaign 06E064000

    Safety recall 06E064000

    Report date
    Component:
    Not available in the source record
    Consequence:
    LACK OF AMBER SIDE REFLECTORS IN THE LAMPS WILL DECREASE LIGHTING VISIBILITY TO OTHER DRIVERS AND MAY POSSIBLY RESULT IN A VEHICLE CRASH.
    Remedy:
    TRADESONIC WILL NOTIFY OWNERS AND REPLACE THE LAMPS FREE OF CHARGE. THE RECALL IS EXPECTED TO BEGIN DURING JULY 2006. OWNERS MAY CONTACT TRADESONIC AT 626-934-8884.
    View authoritative NHTSA record →
  2. Recall campaign 06V092000

    Fuel system

    Report date
    Component:
    Fuel system (FUEL SYSTEM)
    Consequence:
    THIS MAY RESULT IN A FUEL SPILL WHICH IN THE PRESENCE OF AN IGNITION SOURCE COULD RESULT IN A FIRE.
    Remedy:
    DEALERS WILL REPLACE THE FUEL CAP TETHER PIN ASSEMBLY WITH A MODIFIED ONE FREE OF CHARGE. THE RECALL BEGAN ON APRIL 24, 2006. OWNERS MAY CONTACT NISSAN AT 1-800-647-7261.
    View authoritative NHTSA record →
  3. Recall campaign 07E046000

    Safety recall 07E046000

    Report date
    Component:
    Not available in the source record
    Consequence:
    THIS HARNESS WOULD RESULT IN POWER FROM THE TRAILER BRAKE CONTROLLER GOING TO THE TOWING VEHICLE DASH LIGHT CIRCUIT RATHER THAN THE TRAILER BRAKES. THIS RESULT WOULD BE THE LACK OF TRAILER BRAKING WHEN THE TOWING VEHICLE BRAKES WERE APPLIED. IT WOULD ALSO RESULT IN THE TOWING VEHICLES DASH LIGHTS BEING ACTIVATED WHEN THE VEHICLE BRAKES WERE APPLIED. THE FAILURE OF THE APPLICATION OF THE TRAILER BRAKE COULD RESULT IN REDUCED ABILITY TO STOP AND CONTRIBUTE TO A POSSIBLE CRASH.
    Remedy:
    HOPKINS WILL NOTIFY OWNERS AND REPLACE THE ORIGINAL HARNESS WITH A REVISED HARNESS FREE OF CHARGE. THE RECALL BEGAN AUGUST 17, 2007. OWNERS CAN CONTACT HOPKINS AT 800-835-0129.
    View authoritative NHTSA record →
  4. Recall campaign 08V690000

    Airbags

    Report date
    Component:
    Airbags (AIR BAGS)
    Consequence:
    THIS ISSUE COULD RESULT IN THE NON-DEPLOYMENT OF THE DRIVER AND PASSENGER FRONT AIR BAGS IN A CRASH, INCREASING THE RISK OF PERSONAL INJURY.
    Remedy:
    DEALERS WILL REPLACE THE FRONT CZS WITH A REDESIGNED SENSOR. THE RECALL BEGAN ON JANUARY 26, 2009. OWNERS IN THE OTHER STATES WILL RECEIVE EXTENDED WARRANTY COVERAGE FOR THE SENSOR TO 10 YEARS. THESE OWNERS WILL BE NOTIFIED OF THE WARRANTY EXTENSION BY MAIL AND WILL RECEIVE A STICKER TO PLACE IN THEIR WARRANTY BOOKLET EXPLAINING THE EXTENDED WARRANTY COVERAGE. OWNERS MAY CONTACT NISSAN AT 1-800-647-7261.
    View authoritative NHTSA record →
  5. Recall campaign 10E019000

    Suspension

    Report date
    Component:
    Suspension (SUSPENSION)
    Consequence:
    IF THE COLLAR WELD SEPARATES, THE VEHICLE HANDLING WILL DETERIORATE, POSSIBLY RESULTING IN A VEHICLE CRASH.
    Remedy:
    NISSAN WILL NOTIFY OWNERS AND DEALERS WILL REPLACE ANY AFFECTED LOWER LINK FREE OF CHARGE. THE SAFETY RECALL BEGAN ON JULY 12, 2010. OWNERS MAY CONTACT NISSAN AT 1-800-647-7261.
    View authoritative NHTSA record →
  6. Recall campaign 10V075000

    Fuel system

    Report date
    Component:
    Fuel system (FUEL SYSTEM)
    Consequence:
    THIS COULD CAUSE THE VEHICLE TO RUN OUT OF GAS AND STALL IN TRAFFIC, INCREASING THE RISK OF A CRASH.
    Remedy:
    DEALERS WILL REPLACE THE FUEL LEVEL SENDING UNIT INSIDE THE FUEL TANK WITH A NEW ONE THAT HAS A MODIFIED FLOAT ARM. THIS SERVICE WILL BE PERFORMED FREE OF CHARGE. THE SAFETY RECALL IS EXPECTED TO BEGIN ON OR BEFORE MARCH 22, 2010. OWNERS MAY CONTACT NISSAN AT 1-800-647-7261.
    View authoritative NHTSA record →
  7. Recall campaign 10V517000

    Safety recall 10V517000

    Report date
    Component:
    Not available in the source record
    Consequence:
    THIS COULD CAUSE ENGINE STALLING INCREASING THE RISK OF A CRASH.
    Remedy:
    DEALERS WILL REPLACE THE ECM RELAY INSIDE THE IPDM ASSEMBLY. THIS SERVICE WILL BE PERFORMED FREE OF CHARGE. THE SAFETY RECALL BEGAN ON DECEMBER 6, 2010. OWNERS MAY CONTACT NISSAN AT 1-800-647-7261.
    View authoritative NHTSA record →
NHTSA Consumer Complaints Snapshot 2026-09-07 Open source record

Complaint counts reflect self-selected reports and are not normalised for production sales volume. We publish no reliability scores, superlatives, or vehicle rankings.

What owners actually wrote

Short excerpts from the public NHTSA file. Look for the same symptom repeating.

Data: NHTSA Office of Defects Investigation · snapshot 2026-09-07
Safety incident filters
Showing 10 of 611 complaints · page 1 of 25
2026-04-01Engine (ENGINE)
NHTSA ODI 11728571
CrashFireInjuryDeath
See attached document for complaint.
2026-04-01Fuel system (FUEL SYSTEM)
NHTSA ODI 11728559
CrashFireInjuryDeath
Whenever I fill ip the tank I get a fuel smell inside the vehicle. I do not overfill the tank and always stop filling when the fuel pump stops the first time. I have not been able to identify a leak and have not seen fuel leaking under the vehicle. The smell is strong for about the first 1/4 tank of use.
2026-02-24Electrical (ELECTRICAL SYSTEM)
NHTSA ODI 11720086
CrashFireInjuryDeath
The truck has been stalling while driving or won't start. The ECM relay was recalled and was taken care of Thursday, February 19. However, the truck still stalls while driving and won't start at times. I've asked Nissan to look at the IPDM to see if there was any consequential damage, but they won't without paying a fee for a diagnostic test. This is a major safety issue that needs to be fixed. The recall was from 2010, but we have only owned the vehicle since 2024 and had no idea about the recall.
2024-02-12Engine (ENGINE)
NHTSA ODI 11571478
CrashFireInjuryDeath
The contact owns a 2006 Nissan Frontier. The contact stated that the vehicle was leaking oil. The contact stated that the check engine warning light was illuminated. The contact drove the vehicle to a local dealer who diagnosed that the valve cover gasket needed to be replaced. Additionally, the spark plugs needed to be replaced. The dealer later called the contact and informed the contact that the bank #1 and #2 cam sensors and the coil packs needed to be replaced. The contact stated that the dealer later called back and stated that the vehicle was making an abnormal sound and upon performing a diagnostic test, the dealer advised that the timing chain needed to be replaced. The vehicle was not repaired and remained at the dealer. The manufacturer was informed of the failure. The failure mileage was approximately 110,000.
2024-01-28Engine (ENGINE)
NHTSA ODI 11568324
CrashFireInjuryDeath
Truck will turn on once in awhile and I was told it is the ipdm module and that there's a recall on the part. What can I do to get the part sent to me since there is a recall and the mechanic told me that with a recall I can get the part sent to me at no cost to me
2024-01-28Electrical (ELECTRICAL SYSTEM)
NHTSA ODI 11568323
CrashFireInjuryDeath
The truck will start once in awhile has been taken to the shop and they said they ipdm module is the problem and that there's a recall on that part.
2023-10-26Airbags (AIR BAGS)
NHTSA ODI 11552103
CrashFireInjuryDeath
The contact owns a 2006 Nissan Frontier. The contact received notification of NHTSA Campaign Number: 23E012000 (Air Bags) however, the part to do the recall repair was not yet available. The local dealer was contacted and confirmed that parts were not yet available. The contact stated that the manufacturer had exceeded a reasonable amount of time for the recall repair. The manufacturer was made aware of the issue and confirmed that parts were not yet available. The contact had not experienced a failure. VIN tool confirms parts not available.
2023-09-29Airbags (AIR BAGS)
NHTSA ODI 11547382
CrashFireInjuryDeath
The contact owns a 2006 Nissan Frontier. The contact received notification of NHTSA Campaign Number: 23E012000 (Air Bags) however, the part to do the recall repair was unavailable. The local dealer was contacted, and it was confirmed that the part was not yet available. The contact stated that the manufacturer had exceeded a reasonable amount of time for the recall repair. The manufacturer was made aware of the issue. The contact had not experienced a failure. VIN tool confirms parts not available.
2023-04-24Unclassified NHTSA leftover
NHTSA ODI 11518650
CrashFireInjuryDeath
BRITAX E1C199S GROW WITH YOU, CLICKTIGHT The shoulder straps are too low and the head cradle is too high in the harness position. The harness shoulder straps are 2 inches below the red seat-belt guide for the booster. See picture. This is dangerous. See their own pictures on their website of both the boy and the girl who are in dangerous head positions.
2023-03-25Fuel system (FUEL SYSTEM)
NHTSA ODI 11513754
CrashFireInjuryDeath
A gasoline leak has developed on the fuel tank hose fill adapter that is a molded fixture of the gas tank. In which there is no replacement part or fix for the hose fill adapter gasoline leak but to replace the whole gas tank, which cost hundreds of dollars. I alerted Nissan to the problem that a catastrophic situation could occur related to this grave engineering mistake. Because there are millions of people still driving this type of vehicle and others with the same gas tank design. Nissan said that it is not their problem because the vehicle is out of warranty, and there is no recall, on what I believe to be grave danger for all who owns a Nissan vehicle with this type of gas tank design. My opinion is that a warning bulletin or re-call should be issued immediately for this dangerous problem that many motorist may already have.

Frequently asked questions

What are the most common problems on the 2006 Nissan Frontier?

Owners named Fuel system most often — 230 of 611 reports (38%). That is the NHTSA file, not a diagnosis of every vehicle.

Are there recalls for the 2006 Nissan Frontier?

NHTSA lists 7 safety recall campaigns. They were filed about Fuel system, Airbags, and Suspension. Check the VIN at nhtsa.gov; a campaign on this page can still be open on a specific vehicle.

What should I inspect before buying a 2006 Nissan Frontier?

Look up the VIN for open recalls. Check for fuel smell, leaks and whether it starts and idles cleanly. Then skim owner filings for the same symptom and take that list to a mechanic.

Does a high complaint count mean I should skip this year?

No. Counts are reports people chose to file and they are not adjusted for sales volume. YearTell does not publish scores or a list of years to skip. Inspect the vehicle.

EPA Fuel Economy Database Snapshot 2026-08-21 Open source record

Estimated Ownership Cost

EPA fuel economy ratings and annual operating cost estimates

Data: US EPA Fuel Economy Guide · snapshot 2026-08-21
Supported range: 1,000–60,000 miles per year
Supported range: $1.50–$10.00 per gallon
55% city45% highway
Estimate unavailable

EPA fuel-economy data is unavailable for this vehicle.

No estimate is shown when required EPA values are unavailable.

Open Ownership Cost Calculator →

Adjacent Model Years

Immediate preceding and succeeding model year records

NHTSA Consumer Complaints Snapshot 2026-09-07 Open source record

Complaint counts reflect self-selected reports and are not normalised for production sales volume. We publish no reliability scores, superlatives, or vehicle rankings.

Methodology & Data Integrity

Source: NHTSA ODI / recalls, snapshot 2026-09-07. YearTell is not a government agency.

Read our complete data methodology → Sources