It all depends which metric you want to use for innovation.
Efficiency again depends on the type of resource you're looking at. It's clear that heavy oil will always be more difficult to extract, and most of the oil reserves globally, going forward, will be produced increasingly from heavy oil. It all depends on the geological context where you extract this; it depends on whether you're dealing with oil sands or other types of host rock. It becomes very difficult to adopt a single metric for efficiency of production, depending upon what your end product is.
A lot of work has been done trying to identify it specifically by taking measures such as how much you produce in GHGs to produce a certain type of oil, how much in fugitive emissions you have, how much flaring you do in gas production. Again, the metrics are very dependent on the context—