Exxon Mobil Corp. has reportedly held preliminary talks with Pioneer Natural Resources Co. about a possible acquisition of the U.S. shale oil producer, the Wall Street Journal reported on April 7, citing people familiar with the matter.

Discussions between the two companies about a potential deal have been informal, the newspaper said, adding that Exxon executives have discussed a potential tie-up with at least one other company.

Exxon and Pioneer, in separate emails, told Hart Energy they would not comment on market rumors or speculation.

Exxon views Pioneer as a top target to put its "windfall profits to use," the Journal reported, adding that the talks may not lead to formal negotiations and Exxon may target another company.

Exxon last year earned a record $55.7 billion on sky-high oil and gas prices and ended the year with $29.6 billion in cash and equivalents.

The largest U.S. oil producer this week signaled that its first-quarter operating profits dropped about 25% from the fourth quarter of last year, as oil and gas prices eased and refinery maintenance costs rose. Results for the quarter that ended on March 31 are expected to be reported on April 28.

Pioneer, the third-largest producer of oil after Chevron Corp. and ConocoPhillips in the top U.S. shale basin, denied a media report six weeks ago that it was considering an acquisition of smaller rival Range Resources Corp.

It said at the time that it was "not contemplating a significant business combination or other acquisition transaction."