An oil well owned and operated by Apache Corporation in the Permian Basin, viewed on February 5, 2015 in Garden City, Texas. Spencer Platt | Getty Images

Oil prices tumbled on Monday on profit-taking as the market eyed signs of rising U.S. production, though futures remained close to recent mid-2015 highs thanks to last week's decision by OPEC and other producers to extend output cuts. February Brent crude futures were down $1.30, or 2 percent, at $62.43 a barrel by 2:29 p.m. ET (1929 GMT), while U.S. West Texas Intermediate was down 88 cents, or 1.5 percent, at $57.48. Brent hit a two-year high of $64.65 a month ago and has since attracted record investment by fund managers. "Managed money is very long — both futures and options," said Tony Headrick, energy market analyst at CHS Hedging. "If the bulls are not fed, we're subject to a bit of profit-taking that I think we're seeing today."

John Kilduff, a partner at Again Capital Management in New York, said the market could correct slightly, pulling further downward. "We're in a situation where there might not be much more ammunition on the bullish side," he said. The market is continuing to watch U.S. crude production, which is nearing a record high, according to data last week. U.S. output rose in September to 9.5 million barrels per day (bpd), the highest monthly output since 2015, government data shows. On an annual basis, U.S. output peaked at 9.6 million bpd in 1970. Additionally, drillers in the United States added two oil rigs in the week to Dec. 1, bringing the total count to 749, the highest since September, energy services company Baker Hughes said on Friday.

However, the rig count has been stuck in a narrow range since June. American shale drilling pioneer Harold Hamm on Friday told CNBC he sees the plateauing rig count as a sign that, under pressure from shareholders, oil and gas companies are exercising financial discipline. That means drillers will be more cautions about spending to increase their production, the Continental Resources CEO told CNBC's "Squawk on the Street." "That's not the deal anymore, and finally the analysts and everybody else caught on. Shareholders caught on and said, 'We're not going to put money in there just for growth's sake. We want a return, a good return on capital employed,'" he said. U.S. producers were encouraged during 2017 to increase activity as crude prices started recovering from a multi-year price slump after the Organization of the Petroleum Exporting Countries (OPEC) and some non-OPEC producers, including Russia, agreed to production cuts a year ago. Last week the producers agreed to extend those cuts of 1.8 million barrels per day (bpd) until the end of next year.