Do any 'standard SUV' in rental company have a third row?

At my rental branch (Enterprise), it depends more on the individual car than the size class. But any vehicle that has a third row will probably be considered a "large SUV" or a minivan. Such cars include the Dodge Journey (not all of these are 3-row, however), the Suburban, Tahoe, Buick Enclave, Escalade, and so on.

There are some other types of cars that have 3 rows of seats, such as the Ford Flex and the Mazda 5, Mazda CX-9 and the Ford Taurus X. Cars of this type are usually called "crossovers" and how they are categorized varies from rental company to rental company.

Of these, the Ford Flex probably has the best gas mileage (about 25 mpg highway). For big SUVs like the Suburban and the Escalade, mileage is more like 14-16.

Not all of these cars are available in all markets, so talk to your rental agency about what you need.