Prei Khmeng style refers to the period squeezed between the mid-7th-century, Sambor Prei Kuk era and the early 8th-century Kampong Preah category, corresponding to the suspiciously long reign of Jayavarman I.(1) This period then covers the later sites at Sambor Prei Kuk (Prasat Tao) and certain temples around the king's later capital Purandarapura, located in the area west of Siem Reap. A string of small sites identifiable from inscriptions and lintels as Prei Khmeng period can also be found closely following modern-day National Route 6 between Kampong Thom City and Skun (Skuon).
The eponymously named type site, Prasat Prei Khmeng (Boeng Khnar), is situated to the west of the Thnal Baray but all relics found there are now in museums or storage and there's nothing to be seen at the site itself. Ditto Prasat Ak Yum and other contemporary sites in the area, so it can be quite hard to find many Prei Khmeng reliefs outside of museums.
Brick is still the preferred temple building material with stucco decoration and sandstone lintels and colonettes although the flying palace and octagonal tower innovations appear to have fallen from favour by this date. Colonettes are rounded but feature more decorative rings than before while lintel style is heraldic but generally simpler and less cluttered than Sambor Prei Kuk style. Figures usually replace the makaras and fill the medallions. (The Prei Khmeng category is essentially an architectural style - Andet style refers to sculptures.)
Our lintel examples below come from Prasat Kok Roka (Kampong Thom) (a much later site but with a re-used 7th-century lintel over the south door, the aforementioned Prasat Tao and another uncovered at Angkor Borei and now in the local museum.
 Several historians have even suggested the existence of a Jayavarman Bis or Jayavarman 2 while others place Bhavaravarman II in this category. Assigning an earlier date to Jayavarman III is another solution.