Determining the deadliest venom in snakes is not simply a matter of putting up a list of snakes and pointing to the top ten or twenty. There are a lot of different factors to take into consideration. For instance, snakes release different amounts of venom when and if they bite. A baby rattlesnake is much more deadly than an adult rattlesnake since it doesn’t have control on venom release and tends to inject huge amounts of venom. This suggests the same snake may be more or less deadly depending upon age.
Another potential issue is the definition of "deadliest" venom means. Does this mean deadliest to people, animals, birds, etc? Most venom tests are conducted on mice, and obviously not on people. In fact scientists have long relied on the Lethal Dose 50% (LD50) test, which injects mice with various venoms to determine how quickly they’ll die. These results may be extrapolated to humans, but the numbers don’t add up. Those snakes with the deadliest venom as determined by LD50 tests tend to be involved in fewer human deaths; many of them are shy and less aggressive. Other scientists are concerned with the administration of the LD50 test in any case. Where and how you inject the mice (intravenously, subcutaneously, intramuscularly) might have an effect on how quickly a mouse dies from an injection of venom, and obviously the amount of venom injected may differ significantly from the amount a snake would inject.
With that being said, it’s definitely difficult to determine exactly which snakes have the deadliest venom, and whether this means they are the most deadly snakes. "Most poisonous venom" doesn’t translate to "most dangerous" to humans, although it’s certainly not a good idea to pick up any snake that could potentially give you a fatal bite. In fact, we’d argue that avoiding any snake, even if a bite wouldn’t prove immediately fatal, is a good plan of action.
According to various LD50 tests, the inland taipan found in Australia, and the Russell’s viper found in Southeast Asia likely are nearly tied for land snakes with the deadliest venom. The Russell’s viper is indicated in many more human attacks, since it can live near human habitations and is aggressive. In Myanmar, where the snake frequently comes into contact with humans, a bite causes a 9% chance of fatality, but it also can cause numerous medical problems including kidney failure and failure for the body to properly coagulate blood. Dialysis is often needed in order to help the kidneys and even when kidney dialysis is used, people may still die.
In contrast, the inland taipan in Australia is more potentially lethal to humans. The snake may have one of the deadliest venom counts in the world, but little is known about its action on humans because it rarely bites them and is very shy. The top deadliest venom in the world comes from the hook-nosed sea snake, according to LD50 tests. These snakes are seldom if ever aggressive and few bites from them have ever been reported.
Other snakes with deadly venom include the black mamba, the Indian krait, the tiger rattlesnake, the puff adder, and the forest cobra. The contention that the snakes with the deadliest venom all come from Australia is not true, and you are much more at risk from an aggressive snake that lives near humans than you are from relatively shy snakes, even if they’re more poisonous on the LD50 scale.