Should I book one-way or multi-city?

Always search 'Multi-City.' It protects you under one ticket reference number, which is helpful if one of your regional connections is delayed or canceled.

Is it cheaper to fly or take buses?

Buses are cheaper ($20-$40), but flying saves 10-15 hours of transit time between major hubs. If you have less than 3 weeks, prioritize flights.

Booking a Multi-City Flight Route Through Southeast Asia

Use a 'Multi-City' search tool on a major booking engine to avoid booking three separate one-way tickets, which are often significantly more expensive. Prioritize flying into Bangkok, then using low-cost carriers for the legs to Vietnam and Cambodia to keep transit times under four hours.

Map your sequence. Book your long-haul flight into Bangkok (BKK) first. Thailand has the most international connections and lowest entry costs. Route your sequence as Bangkok -> Siem Reap (REP) -> Ho Chi Minh City (SGN) -> Bangkok/Home to minimize backtracking.
Use the Multi-City search engine. Go to Google Flights or Skyscanner and select the 'Multi-City' tab. Input all three segments at once. This ensures the airline alliances or codeshare agreements are factored into the price.
Account for regional low-cost carriers. If the multi-city tool shows a high price, search for the regional legs (Siem Reap to SGN) separately using carriers like AirAsia, VietJet, or Bangkok Airways. These are often cheaper and aren't always surfaced in global multi-city search aggregators.
Check baggage policies. Low-cost carriers in Southeast Asia charge for everything. When booking, add your checked bag during the initial purchase; adding it at the airport counter can cost double the price.

Should I book one-way or multi-city?: Always search 'Multi-City.' It protects you under one ticket reference number, which is helpful if one of your regional connections is delayed or canceled.
Is it cheaper to fly or take buses?: Buses are cheaper ($20-$40), but flying saves 10-15 hours of transit time between major hubs. If you have less than 3 weeks, prioritize flights.