Americans are paying more than $4 a gallon for gas for the first time, Reuters reports. The national average reached $4.005 per gallon today, up from $3.67 last month and $3.10 last year. Prices had stabilized last week, until crude oil futures jumped to record levels. In a recent survey, 74% of Americans vowed to change their driving habits in response to $4-a-gallon gas. (More gas prices stories.)