What exactly is a blender? I take it that some companies just blend motor oils and do not produce their own basestocks. I take it that companies like Chevron and Exxon/Mobil are big enough to produce their own basestocks and formulate their own motor oils. And they are probably also able to do a lot of testing of their own motor oils. What about the blenders? I take it that they are smaller companies. Somebody mentioned recently at this web site that Castrol is a blender. I always thought that Castrol was a large company able to produce its own basestocks and able to do its own research and development. So if Castrol is a blender, who produces the basestocks for Castrol? British Petroleum? Is Pennzoil a blender? How about Valvoline, Quaker State, Redline, Schaeffer's, Kendall, Amsoil, Royal Purple, etc.? Are the blenders able to do a lot of research on their motor oils? Are they able to control the quality of basestocks that they buy?