I wouldn't worry too much about it, it sounds like the $4 a gallon figure is media speculation. The pipe break was last night and gasoline futures are still trading around 2.25 on the NYMEX - that's probably 2.90 a gallon at the pump, depends on where you live. I paid 3.17/gal for premium and that was 24 hours after the pipe shutdown.
This break won't affect prices as much as you might think - most oil is bought on the futures market, and futures prices are currently higher than spot prices, which is almost unheard of in trading. This means that suppliers are holding a lot of oil in reserve, because they can sell their oil for significantly more money 9 months down the line then they can sell it for tomorrow.
The oil to replace this 8% will come directly from the spot market, raising spot market prices to a more reasonable level (higher) in line with futures prices, but not necessarily jacking up the futures price (that most oil buyers buy at) by a significant amount (more than a few cents).
4 dollar a gallon gas is, in the current situation, largely a figment of the media, oil speculators, and people who would like to see America's changeover from fossil fuels accelerated by high prices.
You can keep an eye on price hikes over at the
NYMEX , that's the New York Mercantile Exchange, or the market where a significant chunk of the world's gas and oil is bought and sold. They're kind of like the "canary in the mine" for street level price increases.