Assuming 30 trading days horizon, S&P 500 is expected to under-perform the Tesla. But the index apears to be less risky and, when comparing its historical volatility, S&P 500 is 5.55 times less risky than Tesla. The index trades about -0.05 of its potential returns per unit of risk. The Tesla Motors Inc is currently generating about 0.17 of returns per unit of risk over similar time horizon. If you would invest  8,759  in Tesla Motors Inc on May 20, 2013 and sell it today you would earn a total of  1,580  from holding Tesla Motors Inc or generate 18.04% return on investment over 30 days.