Genome replication is a crucial and essential process for the continuity of 
life.In all organisms it starts at a specific region of the genome known as 
origin of replication (Ori) site. The number of Ori sites varies in prokaryotes 
and eukaryotes. Replication starts at a single Ori site in bacteria, but in 
eukaryotes multiple Ori sites are used for fast copying across all chromosomes. 
The situation becomes complex in archaea, where some groups have single and 
others have multiple origins of replication. Themococcales, are a 
hyperthermophilic order of archaea. They are anaerobes and heterotrophs-peptide 
fermenters, sulphate reducers, methanogens being some of the examples of 
metabolic types. In this paper we have applied a combination of multiple in 
silico approaches - Z curve, the cell division cycle (cdc6) gene location and 
location of consensus origin recognition box (ORB) sequences for location of 
origin of replication in Thermococcus onnurineus, Thermococcus gammatolerans and 
other Themococcales and compared the results to that of the well-documented case 
of Pyrococcus abyssi. The motivation behind this study is to find the number of 
Ori sites based on the data available for members of this order. Results from 
this in silico analysis show that the Themococcales have a single origin of 
replication.