Multiphase meters are relatively new on the market. Since this generic technologies first appearance on the market there have been significant improvements. This is encouraging for the hydrocarbon production industry as the list of potential applications where such a proven technology could be utilized is growing steadily. Some use and fully trust these technologies in the operating envelope they were designed to work within and are satisfied with the meters performance. Some still view these technologies as exciting new systems, but systems which are still under development and under field trial. It is clearly true that the manufacturers are still developing their products. This can be seen in the relatively recent development where the multiphase meter technologies were developed to attempt to close the gap between the upper liquid loading limit of the multiphase meter and the lower liquid loading limit of the wet gas meter (as shown in figures). operate in wet gas flow. In fact, whether a multiphase meter is the final product or still being developed appears to largely depend on the particular application. The generic multiphase meter, with its DP primary element and phase fraction systems, relies heavily on the flow model used and the data set derived correlating factors to account for slip between the phases. With flow conditions where the meter has been extensively tested and checked with test data from the multiphase and wet gas flow facilities the system can be said with justification to be fully market ready. It is with flow conditions out with these data sets that the debate of market readiness continues. It is the requirement for this very substantial multiphase flow data set that is at the core of the secrecy of the individual suppliers. The expense of, and the time taken, in gathering these data sets is substantial and hence the resulting correlating factors are naturally guarded closely. The result is industry can not freely scrutinize the flow calculation methodology of the individual marketed meters and therefore they are seen as "black box" technologies. The issue then is it is difficult for users to make an informed decision with regards to the effect of extrapolating the flow models, or more precisely, the slip correlations. The requirement for multiphase meters is wide spread throughout the industry. The range of field conditions is extremely wide and whereas the available multiphase and wet gas test facilities offer significant ranges of flow conditions, even between them, they could never seriously hope to cover the whole range of the hydrocarbon production flow conditions. The pressing issue with multiphase meters and the hydrocarbon production industry is therefore, not do these meters work in principal, but what is the effect on the stated uncertainties when they are taken out side their test data range? Multiphase meters offer great advantages to industry. They are installed successfully in many applications and it is clear that they will continue to develop in the future offering great benefits to the hydrocarbon production industry.