A possible measure of the viability of oil shale as an energy source lies in the ratio of the energy in the extracted oil to the energy used in its mining and processing (Energy Returned on Energy Invested, or EROEI). A 1984 study estimated the EROEI of the various known oil shale deposits as varying between 0.7–13.3; Some companies and newer technologies assert an EROEI between 3 and 10. According to the World Energy Outlook 2010, the EROEI of "ex-situ" processing is typically 4 to 5 while of "in-situ" processing it may be even as low as 2.