The Spaniard said he was hopeful he could finish on the podium in India.
"If the (drivers on the) soft have some problems and people start pitting and go into heavy traffic maybe the race win will be between Webber and me," he said.
"If the soft tyres last longer than expected, it will be difficult to recover places.
"It is in the flip of a coin because no-one knows how the soft tyres will behave.
"On Friday I did 15 or 16 laps with the soft tyre, not in a very good pace, but I did some laps and this morning I did three.
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"Set to set it depends, it is a random tyre and you need to be lucky with the set you put on for the race."
McLaren's Jenson Button, who is starting on the medium tyre in 10th place, said: "There will be interesting strategies and fun viewing, I think. I don't think you're going to be able to overtake that easily.
"For the teams in front (on the soft tyre) it's very difficult to see how it's going to work because they are going to be stuck in traffic. I don't know how happy Sebastian is, but we will see."
Other top-10 drivers starting on soft tyres are Ferrari's Felipe Massa, Lotus's Kimi Raikkonen and Sauber's Nico Hulkenberg in fifth, sixth and seventh places respectively.
The Indian Grand Prix - live on BBC TV, radio and online
Sunday 27 October : Race coverage at 08:30 GMT BBC One & 09:00 GMT BBC Radio 5 live, plus live text commentary online. F1 Forum: 11:45 on selected TVs, online & BBC Red Button. Race repeated at 14:00 GMT on BBC One & 16:00 GMT BBC Red Button. Highlights: 19:00 GMT on BBC Three
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