HOUSTON | 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.

FILE - In this Monday, May 18, 2015, file photo, more than 30 oil drilling rigs are idle in a Helmerich & Payne, Inc. yard along Groening Street in Odessa, Texas, as rig counts drop in the Permian Basin. The drilling boom, driven by high oil prices and new discoveries, brought tens of thousands of workers to oil fields in several states to run drilling rigs and supply the equipment and services needed to produce crude. Then the price of oil tanked, plummeting by half in late 2014 and reaching levels in 2015 not seen since the financial crisis. Oil companies abandoned drilling projects and began laying off workers. (Courtney Sacco/Odessa American via AP, File) MANDATORY CREDIT

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 was down three, Kansas, New Mexico and North Dakota dropped two each and California was off one.

Alaska increased by two rigs and Ohio was up one.

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