At the high end of the scale, and made only in pilot plant quantities so far, are ExxonMobil's new Visom branded Group III+ base stocks. This product aims to meet one of Europe's most difficult engine oil specs, 0W-30. So far, marketers have needed to formulate with polyalphaolefins to meet the stringent cold-cranking, viscosity and volatility requirements of this grade. Visom is created through wax isomerization, and has an impressive viscosity index of 140, thanks to its high paraffin content. (The name Visom was derived from combining "viscosity index" and "isomerization," Cox explained.) The product became possible after the ExxonMobil merger, and combines Exxon reactor hardware with Mobil catalyst technology, with engineering and research support from both. Basically, it upgrades slack wax to base stocks with high V.I., low volatility, excellent cold-cranking properties and what Cox called "superior" blending performance. Visom is primarily iso-paraffins, he pointed out, while competing Group III base stocks made from hydrocracker bottoms have significant naphthene content. He went on to show how Visom's blending advantages and cold-cranking performance mean that 5W-40 engine oils can be made with 100 percent Visom base stock, without resorting to PAO, and at a lower additive treat rate. He also described how 0W-30 requirements can be met with Visom alone or with PAO alone (but not with competing Group III base stocks unless some PAO is included to achieve the cold-cranking limit).