The Israelis are considering the F-16 Block 60, the most advanced version of the venerable Falcon, as part of its option to buy 50 more F-16s for $2 billion under its 1999 contract with Lockheed Martin. While the F-16 Block 60 is clearly superior, it is also more expensive, and the Israelis will only be able to afford it if they receive extra military aid from the US as part of a peace agreement. The option on the F-16s will expire in about a year and if the Israelis don't exercise it, buying the planes later would cost an extra $200 million.--Stephen V Cole