The well, which was drilled to confirm the high gas and gas condensate flow results in the earlier Elk-4 well, flowed gas just before the end of 2008 at rates of up 15 million cubic feet per day while circulating out gas kicks during drilling operations in the upper section of the structure.
InterOil president Bill Jasper said the company was "most encouraged" by the gas flow, adding that it boded well for the well's potential.
"Based on what we've seen to date, we are hopeful that Antelope-1 will eventually go on to become a significant gas discovery."
InterOil said that further testing of the well would be needed to fully assess the size and potential capacity of the Antelope-1 find.
Located on the Eastern Papuan Basin in PPL 238 of PNG's Gulf Province, Antelope-1 has a planned total depth of 2400m and could prove up enough gas to underpin two trains for the $US5-7 billion ($A7-9.8 billion) Liquid Niugini Gas joint venture in the event of a success.
One-third owned by InterOil, Merrill Lynch and Clarion Finanz (through subsidiary Pacific LNG), the JV would ideally like a two-train liquefaction plant capable of producing up to 9 million tonnes of gas per annum and is looking at production in the late 2013, early 2014 timeframe.