If you do not accept the notion of extended drain intervals, then source reduction is likewise a non-issue. Companies promoting extended drain intervals are quick to point out that the amount of used motor oil can be reduced significantly. There is also an immense reduction in the amount of discarded packaging material. There is another environmentally friendly feature offered by synthetics. Due to their lower volatility, synthetics do not boil off or vaporize as much as petroleum motor oils, which can lose up to 20 percent of their mass in the high heat conditions of the internal combustion engine.
Synthetics lose from four to ten percent.
The benefit is clear in the reduction of make-up oil required because vehicles use less oil, however, the emissions factor may be marginal due to the nature of catalytic converters and other components in the dispersion of these vapors. Due to space considerations I'll close with a number of miscellaneous actions for your consideration. Use your local library to find good books on environmental marketing. Jacquelyn Ottman's Green Marketing is one of many excellent volumes on this topic. Consider carrying an extended drain synthetic motor oil for that niche consumer who is wholly dedicated to environmentally friendly lifestyle choices.