Bus travel is the cheapest and most popular means of overland transport between Phnom Penh and Siem Reap. Having lived in Cambodia for a number of years I have had to travel between Phnom Penh and Siem Reap on many occasions by bus. Thetrip itself is no where as bad as some make it out to be. In fact on a good day the trip itself can leave you with one of your memorable experiences of Cambodia. However, as of March 2014, bear in mind that the road is under construction and as a consequence, the trip is likely to take at least 7 hours no matter which bus and what you are told about how long the trip takes. 

At peak times book well in advance(at least 2-3 days) as buses can fill up very quickly. If you are trying to connect from Vietnam from somewhere other than HCMC it can be awkward as the 'system' is not set up for this and the suggestion is that you spend a night in Phnom Penh. Vietnamese hotels may not be able to call Cambodia, and some Vietnamese SIM cards do not connect either, so be prepared to use your own phone, which may be very expensive.

Before You Take The Bus  - Get a SIM Card/Travel By Day

If you are staying in Cambodia for more than a few days the best investment that you can make is gettining a Cambodian SIM card for your mobile phone handset. These are sold in every location in Cambodia on road side stalls and in Mobile Phone shops that are found in every small town and village. Popular Networks with coverage are MobiTel Cellcard, and MetFone. Most come with credit and typically cost between $2 and $8 depending on the amount of credit preloaded. You  may be asked for your passport name and number which is required by the government. A phone will come handy when you arrive at Siem Reap and need to contact your hotel if they have arranged for you to be picked up. Also while in Siem Reap a phone will come in handy for when you do your tour of the Angkor Archeological park where Angkor Wat, Bayon, Ta Phrom and the rest of the temples are located. 

Also be a little careful when taking the night bus. Cambodia is generally safe, but the roads aren't too safe at night. All vehicles travel at a high speed and mixed into the road traffic are herds and the stray water buffalo or calf.  Travelling by night carries a higher chance of accident. As importantly you'll miss the amazing scenery if you leave Phnom Penh after sundown. 

Buying Your Bus Ticket - Avoid the Ticket & Bus Scam 

If you have a lot of luggage then allow your guest house or hotel to arrange your ticket as long as they guarantee that you will be picked up at your hotel door by the pick up service offered free by the better bus companies. Usual practice is for the bus company to send out a minivan to pick you up and bring you to their station/office.

When you buy the ticket from your guest house be-careful about any offers from the staff or management to also book a hotel in Siem Reap for you. These are often Commission Hotels that pay to have guests brought to them. They are usually more expensive, sometimes unpleasant and often far from the town centre.

The general rule is that the farther away you travel and the more expensive your bus the higher the likelihood that you will be Commission scammed. In Vietnamese and Cambodian hotels a member of the hotel team may attempt to sell you a “last minute” package to their “partner” Hotel or Guest House in Siem Reap in order to collect a commission when you try and purchase your bus ticket to Siem Reap. Its almost a certainty that you will be approached at the border crossing with such offers and sometimes by guides on VIP buses.

Siem Reap has good budget guest houses/hotels. The best are Commission Free. Having stayed at Golden Temple Villa which is Comission Free and all round a great place to stay, I can recommend them,  but its not too hard to find good places to stay. A search on tripadvisor and online will turn up many alternatives. Your choice depends on how much you are willing to pay.  

Three other small tips. Buy a large bottle of water and some food before you leave Phnom Penh. Also book a window seat. (Seats on at least some of the buses are reserved. Check when you reserve.) You'l find that the bottle will serve as a great pillow if you learn how to place it between you head and the window.  If you want to have such a great travel by bus, Giant  Ibis bus reclining seats will be very comfort.   

VIP or Not VIP

You'll always be offered  the choice to take a VIP bus. These are usually $4-6 more expensive than a normal bus and typically are only for tourists. The only advantage (primarily for women) is that VIP buses usually come with an on bus toilet. If you are a real traveller then avoid teh VIP bus, chances are that if you take a usual bus you will get to sit next to some real Khmers which in has always been more interesting in good ways than sitting next to a tourist.

There are several bus companies and each has multiple bus times so there is no danger of not being able to catch a bus. Canby which produces very good free print guides (available at most hotels) on Cambodia has a useful page with the departure times of all major bus lines.

Phnom Penh does not have a central bus station. Buses from different companies depart from different stations. If you don't have much luggage its always best to go to the bus station directly and buy the ticket yourself. The whole process is not difficult and if there are several of you then there is a worthwhile saving to be had. The Canby guide page has full details of each station.

In Siem Reap too there is no central station. Each Bus line operates its own depot.  The main Chong Kov Sou bus station is located near Phsar Leu (the 'Upper Market') a couple of kilometers west of town center. On arrival, tuk tuk drivers will swamp you especially if you are on a VIP bus. In most cases these are all Commission Drivers and if you have already booked into a good Siem Reap hotel they will have sent you a tuk tuk free of charge who will be waiting for you at the station. If you already have a driver Be on your guard about any offers from these drivers to take you to a hotel of their choice.

Main Bus Companies 

 Four bus companies offer regularly scheduled daily service between Siem Reap and Phnom Penh:

 (1) Giant Ibis Transport, (2) Sorya Transport 168, (3) Capitol , (4) Mekong Express

 Giant Ibis Transport

 All four are OK. They have different routes to Siem Reap and different stops on the way. The mid range Sorya is the best value. It stops about an hour from Siem Reap. Capitol is much more basic and a few dollars cheaper. Giant Ibis Transport is a new company but it comes up with Brand New Luxury bus which equip with Wi-Fi internet connection, spacoius leg room ( if you are tall you can consider with Giant Ibis), Safety Seatbelt.  GIant Ibis is very convinient to travel if your afford to pay a few dollars more.  Mekong is more expensive by perhaps as much as $4 a ticket but is worth taking if you need an onboard toilet. 

Arrival In Siem Reap

Chances are that the earliest that you will arrive in Siem Reap is 6pm when the sun has already set and you'll be feeling a bit tired and uncertain. This is where your Cambodian Mobile SIM Card is will be invaluable. If you already have a SIM about an hour before you arrive you can call your hotel reception and confirm that they have dispatched a free pick up for you. Should you not have arranged a pick up from your guest house or if you cant find your driver then the phone will again come in handy. You can call your hotel and they will usually try their best to get a driver to you.

If you haven't booked and its high season then you'll find a phone and a guidebook the best way of getting a room at a good hotel. Doing a tour around town to find a room isn't the best idea in Siem Reap - especially during high season.