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Our tech writer did a piece on this. I finally remembered to dig it up. Here are his pertinent comments:

"Gates Corp. warns that all rubber products have a limited life on a given application. Service life can be adversely affected by:
* External abuse, such as kinking, crushing, abrasion, or high-end pull
* High pressure or high-surge pressure
* Exposure to higher-than-rated temperatures
Fuel hose has three standards: SAE 30R7 for low pressure, SAE 30R9 for high fuel-injection pressure, and SAE 30R10, for fuel line that is submerged inside a tank.
According to Gates Corp., at times, more aggressive fuels can extract the oils that give SAE 30R7 hose its flexibility. The result is a brittle, stiff tube that will greatly reduce the performance and service life of the hose.
Fuel-injection hose is designed for low-permeation contact with a wide variety of alcohols, alcohol fuel blends, and diesel fuel. Gates SAE 30R9 hose uses a laminated tube of fluoroelastomer as a thin-wall inner layer backed by traditional compounds. This first layer protects the rest of the hose from attack, swelling, or permeation from aromatics, oxidized gasoline (as can occur in fuel-injection systems), ethanol, oxygenate additives, and a wide range of petroleum-based products.
The laminated tube will resist cracking caused by “sour gas,” which forms when unused gas is returned to the fuel tank. As an added benefit, this hose construction reduces emissions because fuel can’t evaporate through the hose walls.
Therefore, Gates engineers assert that the best choice for automotive fuel line hose applications today is fuel-injection SAE 30R9 hose. For installers, it is the best choice for reduced comebacks and for high-performance, assured trouble-free service in a changing fuel environment.
Points to Consider
Gates Corp. says in systems with a return line to the tank, fuel can go sour quickly from exposure to engine heat. Even if we don’t have a fuel return line, we shut down a truck engine and then leave it for a week or month. The engine heat starts gumming, or souring, or oxidizing—whatever you want to call it—and it has a lot of time to deteriorate because the vehicle is not a daily driver. Maybe the next time that we start the vehicle, we’re feeding the worst gas in the system into the carburetor. Using STA-BIL year round may help in this scenario.
The other standard, SAE 30R10, is for fuel line that is submerged inside a tank. It has barrier material on both the outside and inside and is made for high fuel-injection pressure..
I checked three lengths of fuel hose in my shop. All were 30R7—the cheap stuff. When it’s time to reorder, I’ll look into 30R9.