Oilfield services company Baker Hughes Inc. says the number of rigs exploring for oil and natural gas in the U.S. declined by 13 this week to 637.

The Houston firm said Friday 510 rigs sought oil and 127 explored for natural gas amid depressed energy prices. A year ago, 1,633 rigs were active.

Among major oil- and gas-producing states, Texas declined by seven rigs; Pennsylvania, three; Kansas, New Mexico and North Dakota, two each; and California, one.

Alaska increased by two rigs and Ohio was up one.

Arkansas, Colorado, Louisiana, Oklahoma, Utah, West Virginia and Wyoming were all unchanged.