In Cochabamba, Bolivia at the moment, and just had my best mileage of the trip so far.
I filled up with gas yesterday after covering 240 miles/386km from La Paz. Took less than 17 litres. That worked out to 54mpg (US), 64.85mpg (UK), or 23 km/l. Not bad for a bike that hasn't had a service in 26,000 miles (ok I cleaned the air filter about 8000 miles ago, and oil changes of course).
Mileage is helped by the high altitude. Average altitude for this section was around 3500m/11500ft. Thinner air means the the injectors squirt less gas into the cylinders - there is a drop in power to go with it, but not unbearably so. The Tenere has power to spare...
Another nice surprise at the gas pump - Bolivia has subsidized fuel, like Ecuador, and price for locals runs about 50c/litre. If you are on foreign plates however, the price is tripled. The girl at the pump yesterday checked my plates, but still charged me the local price. Score!