Some tips for cooking prime rib in the oven include seasoning at least 45 minutes prior to cooking, roasting at a low temperature of around 200 degrees Fahrenheit and using a thermometer to monitor temperature during cooking. To ensure that the prime rib is optimally moist for serving, it is important to let it rest after cooking. This allows the juices released during cooking to be reabsorbed by the meat and not lost by immediate carving.
Salting or seasoning the rib well in advance of cooking has a similar logic behind it to letting the meat rest after cooking. Seasoning the uncooked prime rib draws moisture to the surface, in turn dissolving the salt. The longer the meat is allowed to rest in this way, the more of this salt solution is reabsorbed, which tenderizes the prime rib.
Often, people will roast prime rib at a high temperature to brown the outside of the meat; however, this tends to overcook the outer layers. For this reason, it is preferable to slow roast at a low temperature and then increase the temperature to brown only the topmost layer toward the end of the cooking time. Using a reliable thermometer will aid in knowing when to start browning the outside. For medium rare, the internal temperature should be between 115 and 120 degrees; for medium, it should be between 125 and 130 degrees.