Current full synthetic oils, and bio-synthetic motor oils derived from vegetable oils, already contain biodegradeable base oils.
No motor oil can be totally Green since the additive package contains some components not biodegradeable in the short term.
And once the motor oil has been in an engine, all kinds of hydrocarbons will be mixed into the used oil, making it rather "unfriendly."
Green Oil and so-called "environmentally friendly" oils is mostly a marketing term at this time. What is a "Green Oil," and what does the term "environmentally friendly" really mean?
All oils are biodegradeable to some extent; it is simply a matter of degree as to HOW biodegradeable they are. I.E, how long does it take for bacteria and UV energy to degrade harmful components and base oils.
As far as G-oil availability, my info shows it is only in two forms and one application.
The two forms are 2-cycle oil, and the 10W30 4-cycle. The single application is in outdoor power equipment.