Apart from Texas and North Dakota, oil production from the Lower 48 states is on the decline, OPEC said in its market report for February.

In its review on U.S. oil development, the Organization of Petroleum Exporting Countries said it revised its oil supply down by about 40,000 barrels per day. "It dropped in most states, with the exception of Texas and North Dakota," the February market report, released Monday, stated.

On a quarterly basis, OPEC said fourth quarter production was revised down by 10,000 bpd, with figures for the first three quarters also cut.

"Despite an annual increase in U.S. liquids production, mainly from unconventional sources, namely tight crude [oil] and unconventional natural gas liquids, year-on-year production growth declined over the period," the report said.

Tight crude oil and unconventional gas refers typically to reserves drawn from shale deposits.

OPEC's decision in late November to keep production steady helped advance declines in crude oil prices, off about half of their June value. OPEC said it needed to keep production steady to defend a market share under pressure from increased production from U.S. shale.

Prices are at a point where energy companies are cutting back on the amount of money planned for exploration and production operations. That's been reflected in a decline in the amount of rigs deployed in shale reserve basins.

In a daily report, the North Dakota state government reports 136 active rigs as of Monday, a 29 percent decline from last year and a 33 percent decline from a high-water mark set in 2012.

OPEC in its February report said investors are largely optimistic that oil prices will rebound. Global oil demand is expected to increase by 1.17 million bpd for 2015.