TULSA -- The U.S. trustee overseeing SemGroup LP 's bankruptcy case in Delaware has asked a federal judge to appoint an examiner to investigate the Tulsa company's failed oil-hedging practices and several "insider" financial moves that might have funded those trades.

Tuesday's motion by Trustee Roberta A. DeAngelis noted that many creditors are concerned about SemGroup's "dearth of information" concerning a...