Fyi, when you trade CL, you are not buying/selling light crude barrels. You are just trading an agreement to trade crude oil at specific conditions (price, date, quantity, quality, etc.). If you don't understand the difference, let 1 contract of CL expires...
$50 multiplied by the S&P 500 index. Cash settled. In other words, if you hold an open position into expiry your trading account is debited or credited against the expiry final settlement and the expired contract is zeroed out. The CL contract you mentioned in your OP is physically settled to make or take delivery FOB at the Cushing OK terminal - and you don’t won’t anything to do with that risk. If you fail to close out an open position late into expiry your broker will close out open physical positions for you prior to first notice and charge you a substantial fee for the courtesy. Standard and Poors has an excellent website on the S&P 500 composition and calculation procedure. https://www.cmegroup.com/trading/equity-index/us-index/e-mini-sandp500_contract_specifications.html