The decline of ethane rejection has blown out the price differential between Conway, Kan., and Mont Belvieu, Texas, and signals a southbound pipeline constraint.

“Before additional infrastructure is operational, pricing at Conway is likely to remain relatively weak,” wrote Marissa Anderson, senior energy analyst for BTU Analytics Inc., in a recent report. “In particular, ethane at Conway will likely be related to regional natural gas prices to encourage ethane rejection.”

Mont Belvieu, by contrast, has experienced an upward swing in ethane prices as new petrochemical facilities open on the Gulf Coast, she wrote. That makes it viable to bypass Conway when moving Rockies gas to Mont Belvieu, even with higher transportation costs.