The expansion has increased the pipeline's capacity to meet WA's growing gas demand with an increase in firm full-haul capacity of about 100 terajoules per day.

Construction of Stage 5A began in February and involved installing 570km of parallel pipe, duplicating 50% of the DBNGP mainline.

DBP executive chairman Stuart Hohnen said the stage 5A expansion brought DBP's expansions expenditure to $1.1 billon since taking ownership of the pipeline in October 2004.

"The Dampier to Bunbury Natural Gas Pipeline is the backbone of Western

Australia's flourishing energy economy," he said.

"The Stage 5A Expansion was delivered on time and on budget, in a climate where many projects of this scale suffer delays and cost over runs."

Hohnen said DBP would continue to pursue opportunities to expand the DBNGP into the future where demand for full haul capacity exists.

DBP is majority-owned by Duet Group, with Alcoa and Babcock and Brown Infrastructure as minority owners.