Have you ever heard of anyone on 10 liters of oxygen? I was shocked to hear that a friend was placed on the amount. A different doctor changed it to 5.
I thought it could lead to brain damage to go that high.
Anything under 90% is too low. If he has sleep apnea, he needs to be on CPAP or BIPAP at the minimum. O2 will not do him any good if he isn't breathing! He might be able to have a sleep study in his home, but more than likely they will want him to go to a sleep center. It's not really that bad, I've had 5 and survived. Untreated sleep apnea leads to added work for the heart so it can enlarge and cause heart muscle disease, as well as high blood pressure, arrhythmias, weight gain, etc. It is nothing to fool with.
Your father may have sleep apnea. He can get an overnight sleep study test in his home. If it is sleep apnea, he should probably be put on oxygen at night while he sleeps. The 60's is very low and I doubt that it is safe that low.