Dialects are sometimes quite marked. Notable variations are found in speakers from Phnom Penh (which is the capital city), the rural Battambang area, the areas of Northeast Thailand adjacent to Cambodia such as Surin province, the Cardamom Mountains, and in southern Vietnam. The dialects form a continuum running roughly north to south. The speech of Phnom Penh, considered the standard, is mutually intelligible with the others but a Khmer Krom speaker from Vietnam, for instance, may have great difficulty communicating with a Khmer native to Sisaket Province in Thailand.
Northern Khmer, the dialect spoken in Thailand, is referred to in Khmer as Khmer Surin and, although it only began divergence from standard Khmer within the last 200 years, is considered by some linguists to be a separate language. This is due to its distinct accent influenced by the surrounding tonal language, Thai, lexical differences and its phonemic differences in both vowels and distribution of consonants. Final "r", which has become silent in other dialects of Khmer, is pronounced in Northern Khmer.
Western Khmer, also called Cardamom Khmer, spoken by a small, isolated population in the Cardamom mountain range extending from Cambodia into Thailand, although little studied, is unique in that it maintains a definite system of vocal register that has all but disappeared in other dialects of modern Khmer.
A notable characteristic of Phnom Penh casual speech is merging or complete elision of syllables, considered by speakers from other regions as a "relaxed" pronunciation. For instance, "Phnom Penh" will sometimes be shortened to "m'Penh". Another characteristic of Phnom Penh speech is observed in words with an "r" either as an initial consonant or as the second member of a consonant cluster (as in the English word "bread"). The "r", trilled or flapped in other dialects, is either pronounced as an uvular trill or not pronounced at all. This alters the quality of any preceding consonant causing a harder, more emphasized pronunciation. Another unique result is that the syllable is spoken with a low-rising or "dipping" tone much like the "hỏi" tone in Vietnamese. For example, some people pronounce /trəj/ (meaning "fish") as /təj/, the "r" is dropped and the vowel begins by dipping much lower in tone than standard speech and then rises, effectively doubling its length. Another example is the word /riən/ ("study, learn"). It is pronounced /ʀiən/, with the "uvular r" and the same intonation described above.