As mentioned in the Base Oils & Lubricant Performance thread, Group V ester oils are often formulated into Group IV PAO based lubricants for improved performance characteristics. For more on the performance attributes of ester oils, see Esters in Synthetic Lubricants, a paper by Tom Schaefer. As indicated by Mr. Schaefer, the maximum amount of esters formulated into automotive synthetic motor oil typically does not exceed twenty-five percent. Ester quantities greater than twenty-five percent do little or nothing in the way of increased lubricant performance, only adding to the final cost of the lube; esters are expensive. How expensive are they? Mr. Schaefer was recently asked to speculate on how much a finished quart of Group V 100% ester motor oil would cost. It was theorized that if one such product was researched and developed, the final cost of the lube could be three to four times that of a Group III motor oil. Thatís $20 to $27 dollars for one quart of motor oil as estimated by todayís current prices. When the potential cost of a 100% Group V ester based motor oil is put into perspective, it is no wonder that the motor oil industry has not developed and marketed such a product. As it stands now, many find that a good group III motor meets their requirements and do not deem it necessary to purchase a more costly Group IV PAO based alternative. Still, some enthusiasts dream of the day when one such 100% Group V ester motor oil will exist. Currently, manufacturers of PAO/easter based oils donít openly publish base oil proportions, but itís been said that the rule of thumb for determining ester content in synthetic motor oil is the final cost of the finished lubricant. For example, Amsoil SAE 10W-30 100% Synthetic Motor Oil retails for $8.90 per quart. By contrast, Amsoil Dominator SAE 10W-30 Synthetic Racing Oil retails for $11.10 per quart. Using the rule of thumb in this comparison would reveal that the racing oil is formulated with more ester oil and other top grade additives. So when considering the use of top of the line oil additives, like esters, and the processing required to properly formulate the finished lubricant, this is one area where the final cost for a quart of synthetic motor oil goes up exponentially. For example, compare the costs of Lubricant #2 and Lubricant #3 in the Base Oils & Lubricant Performance thread.