Many tankers ended up idle or used for storage, waiting in anchorages across the country like the dozens of tankers anchored in San Pedro Bay near the ports of Los Angeles and Long Beach.
In 2020, U.S. imports of total petroleum and of crude oil were at the lowest levels since 1991. This decrease in U.S. imports may help explain the decline in the number of observed tanker vessels. Only 21 of the top 25 tonnage ports have observed tanker vessel calls. The liquid bulk terminals at these 21 ports had 16,692 observed vessel calls in 2020, down 391 (2.3 percent) from 17,083 in 2019.
As shown in the figure below, average tanker vessel dwell times at these top ports was estimated at 41.4 hours in 2020, down almost two hours from 43.3 hours in 2019. In general, tanker dwell times were about a third longer than container vessel dwell times, most likely because it takes more time to pump petroleum and crude oil than to lift shipping containers from a vessel of similar size.
In the first half of 2021, average tanker vessel dwell time decreased to 40.4 hours. The 21 liquid bulk ports had 7,208 observed vessel calls during the same period in 2021, down 2,441 (25.3 percent) from the same period in 2020. Since 2018, tanker vessel dwell times have improved by showing a general downward trend.
Average tanker dwell times for individual ports are shown in the online Port Profiles.
 U.S. Department of Energy, Energy Information Administration, Oil & Petroleum Products Explained: Oil Imports & Exports (April 2021), available at https://www.eia.gov/ as of November 2021.
 The ports of Cincinnati-Northern KY; Huntington-Tristate, KY, OH, WV; Mid-Ohio Valley Port, OH and WV; St. Louis Metro Port, IL and MO are located on rivers and may handle primarily liquid bulk barges, which are not equipped with AIS and thus not included in the tanker dwell times. U.S. Department of Transportation, Bureau of Transportation Statistics, calculated using AIS data from the U.S. Coast Guard’s Nationwide Automatic Identification System (NAIS) archive, processed by U.S. Army Engineer Research and Development Center, Coastal and Hydraulics Laboratory, through the AIS Analysis Package (AISAP) software package, as of December 2021.
 The top 25 tonnage ports are based on 2020 port rankings and calculated using 2021 AIS data from the sources cited above.