May 21 (Reuters) – U.S. energy firms added oil and natural gas rigs for a fourth week in a row as higher oil prices prompt some drillers to return to the wellpad.

The oil and gas rig count, an early indicator of future output, rose two to 455 in the week to May 21, its highest since April 2020, energy services firm Baker Hughes Co said in its closely followed report on Friday. RIG-USA-BHIRIG-OL-USA-BHIRIG-GS-USA-BHI

The total rig count was up 137 rigs, or 43%, over this time last year. It was also up 86% since falling to a record low of 244 in August 2020, according to Baker Hughes data going back to 1940.

U.S. oil rigs rose four to 356 this week, their highest since April 2020, while gas rigs fell one to 99.

U.S. crude futures were trading below $64 a barrel on Friday, putting the contract up about 31 % so far this year after they dropped about 21% last year.

With prices mostly rising since October 2020, some energy firms have said they plan to boost spending in 2021 after cutting drilling and completion expenditures over the past two years.

That spending increase, however, remains small as most firms continue to focus on boosting cash flow, reducing debt and increasing shareholder returns rather than adding output.

Enverus, a provider of energy data with its own rig count, said the number of active rigs in the week dropped 21 to 517 as of May 19.

Enverus said the “wild week-over-week swing” was likely due to rigs moving between wells and noted the rig count in the Bakken in North Dakota rose to 18, its highest since last May.

U.S. oil output from seven major shale formations, including the Bakken, is expected to climb by 26,000 barrels per day (bpd) in June to 7.73 million bpd, the first rise in three months, the U.S. Energy Information Administration said in a monthly forecast on Monday. (Reporting by Scott DiSavino Editing by Marguerita Choy)