Britain’s refineries are unable to cope with the growing demand for diesel, leaving the country increasingly reliant on imported stocks.

That’s according to a new report from motoring research group the RAC Foundation, which says that demand for diesel has risen by 76 percent in the past 20 years, from 12.9 to 22.7 billion liters. Over the same period, demand for gasoline decreased by 46 percent.

By 2030, diesel is predicted to be outselling gasoline by four liters to one.

Yet this increased demand for diesel cannot be met without importing significant quantities of the fuel. Although the U.K. remains a net exporter of gasoline, it became a net importer of diesel in 2006 and in 2013 imported over 45 percent of its requirements.

Britain’s growing dependence on imports is partly down to the closure of refineries. In 2009 there were nine large refineries across the country, but today there are just six and several of these have been or are up for sale.

The RAC Foundation also pointed out that some of the older refineries are configured to produce gasoline rather than diesel — and retrofitting them to produce more diesel is very expensive and often not commercially viable.

Steve Gooding, director of the RAC Foundation, explained:

“Most of our refineries — some of which are more than half a century old — were built when diesel was a niche product. Retrofitting them is a billion pound decision that has failed to stack up for investors who see refining as a low margin business despite our sky-high pump prices. The result: since 2009 three U.K. refineries have closed, and others have been up for sale.”

Relying on imports leaves Britain “at the mercy of the global market”, Gooding warned.