Gurrib, Ikhlaas, Elgilani Elsharief, and Firuz Kamalov. 2020. “The Effect of Energy Cryptos on Efficient Portfolios of Key Energy Listed Companies in the S&P Composite 1500 Energy Index”. International Journal of Energy Economics and Policy 10 (2):179-93. https://econjournals.com/index.php/ijeep/article/view/8676.