What is the ratio for 2.6 ounces of 2 cycle oil with a gallon of gasoline?

Divide the number of ounces in a gallon of gasoline by the number of ounces of oil (both fluid measurements). 128/2.6=49 (about) Essentially this is a 50:1 mix.

Conversely if you want a 50:1 mix divide 128 by 50. Answer is 2.56. for 2 gallons 256/50=5.1 ounces. 2-1/2 gallons of gas will take 6.4 ounces of oil.