1) No known species of reindeer can fly. But there are 300,000 species of living organisms yet to be classified, and while most of them are insects and germs this does not *completely* rule out flying reindeer that only santa has ever seen. 2) There are 2 billion children (persons under 18) in the world. But since Santa doesn't (appear) to handle the Muslim, Hindu, Jewish and Buddhist children that reduces the work load to 15% of the total- 378 million according to the Population reference Bureau. At an average census rate of 3.5 children per household, that's only 91.8 million homes. One presumes that there is one good child in each. 3) Santa has 31 hours of Christmas to work with thanks to the different time zones and the rotation of the earth, assuming that he travels from east to west, which seems sensible. This works out to 822.6 visits per second. This is to say that for each Christian household with good children, Santa has 1/1000th of a second to park, hop out of the sleigh, jump down the chimney, fill the stockings, distribute the remaining presents, eat whatever snacks have been left and get back up the chimney into the sleigh and move on to the next house. Assuming that each of these 91.8 million stops are evenly distributed (which we know to be false but for the purposes of our calculations we will accept), we are now talking about .78 miles per household, a total trip of 75.5 million miles, not counting stops to do what most of us do at least once every 31 hours, plus feeding etc. This means that Santa's sleigh is moving at 650 miles per second, 3000 times the speed of sound. For purposes of comparison, the fastest man-made vehicle on earth, the Ulysses space probe moves at a poky 27.4 miles per second - a conventional reindeer can run , tops, 15 mph. 4) The payload on the sleigh adds another interesting element. Assuming that each child gets no more than a medium sized lego set (2lb), the sleigh is carrying 321,000 tons, not counting Santa, who is universally described as overweight. On land, the conventional reindeer can pull 300lb. Even granting that "flying reindeer" (see #1) could pull 10 times there own weight we cannot do the job of 8 or even 9. We need 214,200 reindeer. This increases the payload- not counting the weight of the sled- to 353,430 tons. Which is 4 times the weight of the Queen Mary (the ship). 5) 353,000 tons traveling at 650 miles per second creates enormous air resistance- this will heat up the reindeer in the same fashion as space crafts re-entering the earth atmosphere. The lead pair of reindeer absorb 14.3 QUINTILLION (that's 1 million raised to the power 5) joules of energy. Per second. Each. In short they will burst into flames, exposing the reindeer behind them, and create deafening sonic booms in their wake. The entire reindeer team will be vaporized within 4.26/1000 of a second. Santa, meanwhile, will be subjected to centrifugal forces 17,500.06 times greater than gravity. A 250lb Santa (which seems ludicrously slim) would be pinned to the back of the sleigh by 4,315,015 pounds of force (g's) In conclusion: If Santa *did* deliver presents on Christmas eve he didn't do it for very long and he only did it once.