Standing beside a Propel Biodiesel pump on Westlake Avenue on Monday, Sen. Patty Murray invoked what's become a standard theme in supporting the alternative-fuel industry: patriotism. Murray argued that by importing oil to fuel our vehicles (gasoline and standard diesel are both made from petroleum), we give money to foreign governments that in some cases would do us harm. The problem is, even green-fuel sellers like Propel still sell oil, and lots of it. If you filled up at the Propel station where Murray stood, 80 percent (or more) of what went into your tank would be standard diesel made from crude oil. Murray arrived at Propel in an Infiniti SUV (which gets about 15 miles per gallon) to push a $1-per-gallon tax credit for companies that make the fuel sold at biodiesel pumps. Congress enacted such a credit in 2004, but it expired in January. A renewal of the credit is attached to the unemployment extension bill that's likely to be voted on this week in the Senate. The tax credit is needed to make biodiesel cost-competitive with standard diesel, says the National Biodiesel Board. Right now, without the credit, biodiesel costs about 45 cents more per gallon at the pump than standard diesel. But even if the credit is renewed, it will only have a small impact on our oil dependence, since the majority of the fuel at Propel's pumps comes from crude oil. Propel spokesperson John Williams says that's mostly the fault of car manufacturers: "If something goes wrong and you've been using [biodiesel that is less than 80 percent petroleum], the vehicle manufacturer could say 'Sorry, your warranty is voided.'" Between that and the small number of passenger cars on the road that use diesel (about 2.5 percent, according to Newsweek), this tax credit doesn't really look like the key to ending our oil addiction. That will probably require spending less time in gas-guzzling SUVs.