Tesla will be added to the S&P 500 index on December 21. With its current market cap the stock will be just over 1% of that index. However, this works out to potentially over $50 billion worth of Tesla stock that S&P-tracking assets will have to buy once its added.
Apple is currently the largest stock in the S&P 500, with a weight of about 6.5% of the index.
The Motley Fool : Here's What's Pushing Tesla Stock Toward $600 -- and Beyond
Yahoo Finance : Top 10 S&P Holdings