The London-listed Anglo-Australian giant, which is better known for its mining than oil operations, submitted a $624m (£490m) cash offer for a 60 per cent controlling stake in the joint venture to complement its royalty bid. BP offered $604m.
BHP Billiton will be the operator of the block, which is less than 50 miles from the US-Mexico maritime border.
The company is obliged to make a minimum investment of $570m and will offer additional royalties of four per cent, which rival BP also matched.
The project is the first joint venture in Pemex's 78-year history and an agreement is expected to be finalised within 90 days.
"This opportunity aligns with our strategy of owning and operating Tier-1 assets and provides an opportunity for BHP Billiton to leverage its industry leading deepwater drilling, development and operational expertise to create value in Mexico," said Steve Pastor, BHP Billiton's president for petroleum operations.
The FTSE-100 listed group's share price closed up 2.7 per cent to 1,339.5p today.
Bids for 10 other deepwater blocks up for auction in the Gulf of Mexico are due to be opened imminently.