Originally Posted by AndyL
Actually looking at those numbers, Webber's advantage is only slight.
The McLaren and Mercedes cars all have the Spa and Suzuka engines with only 1 race on them, so for Korea, Brazil and Abu Dhabi they could be using engines on their 2nd, 2nd and 3rd races respectively.
Webber has at least 2 races on all the 7 engines he's used, but with 1 unused he'll do the last 3 races using engines on their 1st, 2nd and 3rd races.
Vettel has the Suzuka engine with one race on it, and some from earlier in the season with 2 races each. So his last 3 races will be using engines on their 2nd, 3rd and 3rd races.
Massa has the Spa engine with 1 race on it. The Monza engine has 1 race plus Singapore qualy on it, but since it was changed I'd assume it won't be re-used, even though it would be allowed at the final race. He has a couple of other engines with 2 races on them. So having taken the penalty he's in the same position as Vettel now.
Alonso has the Spa engine with one race, plus only one other with 2 races, so he's looking at using engines on their 2nd/3rd/3rd races too. But he's more vulnerable if he loses an engine, because he could have to choose to either take a penalty or make an engine last 4 races.
The guys with the real advantage are Reubens plus the two Renaults. They all have their Suzuka engines with only 1 race, plus a fresh one, so they'll be doing 1st/2nd/2nd for the remaining races. Shame for Reubens that his is only a Cosworth :)
(For several drivers engine 1 has only done one race, but I'm guessing that will have been used for practices since.)
Edit: I just realised that Webber, who's only used 7 engines, is actually more vulnerable in the event of an engine failure than the 4 Mercedes-engined cars. If, hypothetically, they all use their least-used engines in Korea and all blow them up during the race, then the Macs/Mercs would still be have 2nd race/3rd race engines for Brazil and Abu Dhabi. Whereas Webber would fall back to 3rd/3rd because all his other engines have 2 races on already.