Feb 23 (Reuters) - U.S. shale producer Pioneer Natural Resources on Tuesday reported a better-than-expected gain of $177 million for the fourth quarter as crude oil prices improved from pandemic-driven lows. Pioneer reported earnings of $1.07 per share, while analysts expected earnings of 68 cents per share, excluding one-time items, according to Refinitiv estimates. The company reported adjusted earnings of $2.36 per share for the fourth quarter of 2019. (Reporting by Jennifer Hiller Editing by Marguerita Choy)