Will Ethanol-Free (Pure Gas) be okay for 2011 Prius?

It's fine. I'd be more concerned about too much ethanol versus too little. In fact @Mendel Leisk has used ethanol-free before if I'm not mistaken.

 

Safer? No, but not less safe either. Better? Typically 3% better MPG, not enough to offset the typically higher cost, otherwise no meaningful difference.

The main thing it will do is lighten your wallet. The car itself will be just fine.

In theory, if your source has low sales volumes and slow turnover, it could collect more water before it even reaches your car. Lacking ethanol, over a long time it could accumulate in your tank and potentially lead to fuel line freezing in cold weather. This is why, in the old days, some cold climate drivers added HEET or other gas line driers to their tank. I don't believe ethanol fuels have as much problem with this, but can have other problems from stale fuel or slow turnover supply chains.

 

As fuzzy1 hints, the best gas in town is the cheapest, as that turns over fastest, so has not sat underground long.

 

Agree with the others. The car won't care much either way, but your wallet will.

 

Yeah a couple of times I tried letting it go pretty low and filling with Chevron's 94 octane gas. In Canada at least, while all the other pumps say "may contain up to 10% ethanol", the 94 octane pump says "contains no ethanol".

The outcome though, was no appreciable difference in mpg. I'd suspect it helped some, but so minor as to be "lost in the noise". Perhaps too: 94 octane is detrimental to mpg, negated the ethanol-free factor??

 

While higher octane can certainly have lower energy content, depending on refinery- and batch-specific details that are not disclosed to consumers, I don't believe it is comparable to the 3% ethanol difference. Therefore I'll vote for it being mostly "lost in the noise", which can very easily exceed 3%.

Back to the OP, all these engines, or at least their parents or grandparents, were originally designed for just pure gas. Changes to allow 10% ethanol were added later, but pure gas was never completely removed from the market even in North America, let alone the Rest Of World. I've never heard of any design or accessory changes that rendered today's engines unsuitable for straight gas.

 

Toyota’s position is in the Owner’s Manual (PDF), “Fuel information,” pages 578–580, which references ASTM D4814 and the Worldwide Fuel Charter and states, “Toyota does not recommend blended gasoline” but clarifies that “oxygenate blended gasoline where the oxygenate content is up to 10% ethanol” is allowed, provided “it has an octane rating no lower than 87.”

See also Chevron Products Company, Motor Gasolines Technical Review (PDF), 2009, pages 53–60, and SAE J312 and J1297.