as the unit of measure changes, so does the molecular volume.
for any given ratio,...1 once of oil compared to 30 ounces of gas has the same molecular comparison as 1 pound of oil compared to 30 pounds of gas. all that is need is that both mediums are measured in the same unit of measurement and both mediums are the same from ratio to ratio. ie. both ratios are mixed used the same weight and type of oil and the same octane rating of gas. changing any one character changes the whole picture as you state.