Not everywhere injects oxygen - have not seen it in the UK, however I have seen my LFS add stress-coat.
If you haven't had fish for 20 yrs or more have a look at this link which discusses drip acclimation as opposed to float and drop. It's not as complicated as it sounds or can be done more simply by adding tank water to the fish bag after it has been floated for 20mins or more to equalise the temp. The top of the bag is then rolled over a few times and this traps air so it can continue to float. Add a cupful of tank water every 10-15 mins for an hour so that the chemistry can equalise too. Then net the fish into the tank without adding the bag water as this may be quite high in ammonia if the fish have had a long journey or a stressful one.
Some people do still do the float and drop method but I only do it if I feel the fish are worse off in the travel bag than in acclimatising slowly.
If you haven't had fish for 20 yrs or more have a look at this link which discusses drip acclimation as opposed to float and drop. It's not as complicated as it sounds or can be done more simply by adding tank water to the fish bag after it has been floated for 20mins or more to equalise the temp. The top of the bag is then rolled over a few times and this traps air so it can continue to float. Add a cupful of tank water every 10-15 mins for an hour so that the chemistry can equalise too. Then net the fish into the tank without adding the bag water as this may be quite high in ammonia if the fish have had a long journey or a stressful one.
Some people do still do the float and drop method but I only do it if I feel the fish are worse off in the travel bag than in acclimatising slowly.