Horsepower verses weight...?
Without being more specific, there is almost no way of answering your question. The reason is because the motor that most fits your request is the 110 hp, 787cc, 2-stroke engine which is used in several different applications including boats. The skis come in 3 different sizes, so by their weight, fuel efficiency will be change accordingly.
For some examples: The 2007 RXP, 4-Stroke has a fuel capacity of 15.9 gallons including reserve. At WOT cruising, it will burn about 18.2 GPH. Your total run time, counting reserve is about 53 minutes.
The 1998 XP Limited, 947cc, 2 stroke has a capacity of 14 gallons including reserve. At WOT cruising, it will burn about 14.5 GPH. Your total run time, counting reserve is about 59 minutes.
The 1997 GSX, 787cc, 2 stroke has a capacity of 15 gallons including reserve. At WOT cruising, it will burn about 11.7 GPH. Your total run time, counting reserve is about 1 hour 16 minutes.
I hope that gives you an idea but you can't measure fuel efficiency in these watercraft without knowing what it is your riding, since the weight makes a big part of how big the tank is, how far it will go and how long it will last.:cheers: