Via Instapundit, an email from "Engineering Prof Chris Kobus" (I'm guessing this is he):
Diesel technology is inherently more efficient [than gasoline-engine technology]. . . . If all spark-ignition engines were replaced with diesel, we’d reduce our dependence on foreign oil by almost 50%. As good as hybrids are in terms of fuel economy, hybrid diesels would blow them all away. Locomotives have been hybrid diesels for some time now.