The 2013 Toyota Venza certainly isn't one of the most fuel-efficient vehicles if you're comparing it to passenger cars; but If you're shopping crossover vehicles and want to minimize the hit of $4 (or maybe $5) gasoline, then the Venza is one of the better picks.
While some models this size still come only with a V-6, the Venza offers a choice of a four-cylinder engine or a V-6, and indeed the four does get somewhat better mileage. It's rated at 21/27 mpg in front-drive versions, 20/25 mpg in models with all-wheel drive.
Of course you get faster acceleration with the V-6; it's smoother, too. But the numbers fall accordingly. Front-drive, six-cylinder Venzas earn a 19/26-mpg rating, which drops to 18/25 mpg with all-wheel drive--the added traction adds weight you'll be lugging around all the time, and a premium you'll pay as long as you have the Venza.
As we've noticed in real-world driving, the difference between the two engines does almost vanish if you live in hilly terrain; on mostly level ground or with mostly lighter loads, the four is definitely the green pick.