It is my understanding that modern commercial jets have a glide ratio of approximately 7 to 1.
That is, they can go 7 miles for every one mile they descend. Nowadays it might be even better.
Someone with more wisdom please correct me.
Read this http://www.wadenelson.com/gimli.html
It claims an 11:1 glide ratio for a 767 was achieved by the pilots. It is a story about a jet that ran out of fuel at altitude mid flight and the pilots had to figure out how to glide it to a divert airfield because they had never had training that considered both engines flaming out due to running out of fuel. Great story, had never heard about this one before.