Here are the different sources of oxygen:
Compressed gas cylinders - the green and silver cylinders
Liquid oxygen - comes in big tall containers that look like R2D2
Oxygen concentrators - a machine that uses sieve beds to strip the nitrogen out of room air leaving almost pure O2
Here are some of the portable options based on the above sources:
1) Compressed gas cylinders - availble in small or larger cylinders and also with or without pulse dose delivery
2) Liquid O2 portable units - smallish portable devices that can be delivered via pulse dose or via continuous flow. Pulse dose units are often smaller and/or last longer than continuous flow units.
3) Portable oxygen concentrators - units that are much smaller than the concentrators used in the home. They run on batteries, DC (for use in the car), or AC. Depending on how many batteries you have and how often you are in the car or around power these can give you almost limitless ability to be portable. The downside is some units are bigger than other sources. These are available with pulse dose. The advantage to having pulse dose would be to prolong battery life.
In general using pulse dose with give you the benefit of a smaller unit and/or longer delivery time. Your available choices will depend on many factors: 1) what liter flow you are on, 2) if your breathing pattern will work with pulse dose delivery (a respiratory therapist will test this), 3) the availability of different equipment from your provider, and 4) what your insurance will cover.
I currently am on 1.5 liters per night and occassionally need O2 during the day and with exercise. I also need it during air flights. My current equipment includes a traditional concentrator for home use and a liquid system for portability. My liquid portable is a pulse dose Helios. I like it because it is smaller and lighter than the continuous flow portable that is available. For travel I use a portable oxygen concentrator on the plane.
Hope this helps!
Peace,
Steph