The Mont Belvieu, Texas, hypothetical NGL barrel jumped 5% last week to a 42-month high, driven by sharp increases in the prices of propane and isobutane.

The “barrel” is defined as how much NGL would cost in a 42-gallon (gal) unit if the five components were added to it on a percentage basis that corresponded to their share of the market. It exists as an imaginary gauge to track how NGL prices are performing.

The “barrel” rose 1% at Conway, Kan., to its highest point in three months, but the strength in propane and butane prices was balanced by a 22.3% plunge in the price of ethane to its lowest weekly average level since year-end 2015. That put Conway ethane, at 11 cents per gallon (/gal) 47.6% below its high for the year of 21 cents/gal in early January.