U.S. drillers added 14 oil rigs in the week to March 17, bringing the total count up to 631, the most since September 2015, energy services firm Baker Hughes Inc. (NYSE: BHI) said March 17. During the same week a year ago, there were 387 active oil rigs.

The rig count increase came despite a collapse in crude futures over the past two weeks to a more than three-month low because the rigs activated this week were based on decisions made a couple of month ago when oil prices were higher. U.S. crude futures were at about $49 a barrel on March 17, set for a modest weekly rise after falling 9% last week on concerns production cuts by OPEC was failing to reduce a global glut as U.S. shale producers crank up activity.

Since crude prices first topped $50 in May after recovering from 13-year lows in February 2016, drillers have added a total of 315 oil rigs in 38 of the past 42 weeks, the biggest recovery in rigs since a global oil glut crushed the market over two years starting in mid-2014.

Baker Hughes' oil rig count plunged from a record 1,609 in October 2014 to a six-year low of 316 in May 2016 as U.S. crude collapsed from over $107 a barrel in June 2014 to near $26 in February 2016.

U.S. shale oil production in April was projected to rise 109,000 barrels per day (bbl/d), the biggest monthly rise in six months, to 4.96 million barrels per day (MMbbl/d) as output in the Permian Basin, America’s fastest growing shale oil region, hits another record high, according government data on Monday.

U.S. crude inventories edged down from record highs last week, after nine straight weeks of builds, while overall production was projected to rise from 8.9 MMbbl/d in 2016 to 9.2 MMbbl/d in 2017 and a record high of 9.6 MMbbl/d in 2018, according to federal energy data.

Analysts said they expect U.S. energy firms to boost spending on drilling and pump more oil and natural gas from shale fields in coming years now that energy prices are expected to keep climbing.

Futures for the balance of 2017 and calendar 2018 were both trading around $50 a barrel.

Analysts at Simmons & Co., energy specialists at U.S. investment bank Piper Jaffray, this week forecast the total oil and gas rig count would average 818 in 2017, 937 in 2018 and 1,048 in 2019. Most wells produce both oil and gas. That compares with an average of 729 so far in 2017, 509 in 2016 and 978 in 2015, according to Baker Hughes data.

Analysts at U.S. financial services firm Cowen & Co. said in a note this week that its capex tracking showed 54 E&Ps planned to increase spending by an average of 50% in 2017 over 2016. That expected spending increase in 2017 followed an estimated 48% decline in 2016 and a 34% decline in 2015, Cowen said according to the 64 E&P companies it tracks.