Rex Energy Corp., State College, Pa., said its enhanced oil recovery operations in giant Lawrence field in southern Illinois have the potential to double the field’s output by the end of 2015.

QEP Resources Inc., Denver, said its QEP Energy unit signed definitive agreements to acquire from multiple sellers Williston basin development properties for $1.38 billion.

Ophir Energy PLC said its Fortuna East-1 stepout on Block R offshore Equatorial Guinea has encountered gas in the eastern lobe of the Fortuna complex and has discovered gas in the deeper Viscata exploration target.

Petroceltic International PLC and Melrose Resources PLC will merge to create an independent oil and gas company focused on North Africa, the Mediterranean, and the Black Sea.

Parties to the Isarene production-sharing contract have agreed a formal declaration of commerciality for Ain Tsila gas-condensate in the Illizi basin in eastern Algeria.

Citation Oil & Gas Corp., private Houston operator, will buy oil and gas properties in Kansas from Noble Energy Inc. for $140 million.

Midyear 2012 reserves for Costayaco field in the Putumayo basin of Colombia are up sharply since the end of 2011, said Gran Tierra Energy Inc., Calgary.

Ophir Energy PLC and BG PLC said the Papa-1 deepwater wildcat on Block 3 offshore Tanzania has made the first Cretaceous gas discovery outboard of the Rufiji Delta.

CNOOC Ltd. will acquire Nexen Inc., Calgary, for $15.1 billion as China expands its holdings in worldwide exploration and production operations.

Tethys Petroleum Ltd., Guernsey, UK, said an updated independent evaluation indicates that the company’s Tajikistan land holdings contain an estimated gross unrisked mean recoverable prospective resource of 27.5 billion bbl of oil equivalent, more than the UK North Sea.