I have used citgo gf3 oil for sometime now and im pleased with its performance. Last oil chg. Northstar engine 4680mi. 11 months. Oil looked very clean. I have my own test for oil. I put some oil on a tissue from the dipstick and watch the spot expand if there is any dirt in it the dirt will remain in the middle and the clear oil will appear in the ring. I then take new oil and do the same comparing the two colors, the old sample ring and the new oil,in this case the color was identical and there was no dirt in the middle of the old sample. Not so with my buick riviera 400cu. v8 using quaker state, a sample off the dipstick showed dirt in the middle with the ring good in color. The quaker state web site said that their oil will appear black after so many miles and thats normal. I cant remember what filter I removed from the buick It was not a purolator! (wont venture a guess) but the filter I removed from the northstar was a purolator premium plus. Anyway I changed the oil on the buick to citgo and installed a purolator filter. My second choice for oil would be chevron supreme. I have at this time no second choice for filters. All my oils are 10w30.