The European gas market is being supplied by a series of different gas sources. On the European grid, two main gas categories are defined i.e. the low calorific (Slochteren) and the high calorific gas categories or, more formally, the group L and the group H of the second family of gases which are described under the European standard 437 [1].

Where H gas is common throughout Europe, L gas is distributed in only four countries: the Netherlands, France, Belgium and a small area in Germany. In these countries L gas and H gas are distributed in separate networks. In France, Belgium and Germany the L network is a regional network. In the Netherlands, the L network serves domestic, commercial and small industrial customers while H gas is distributed to larger industrial customers [2].

Within each main gas category, the differences in gas quality specifications can lead to restrictions in interoperability. The gas specifications can be divided in three categories: 

1. the combustion properties, 
2. Gross Calorific Value (GCV) and 
3. additional components.

Especially with regards to combustion properties and gross calorific value blending of different gas streams might lighten the regulation of the gas composition in order to comply with the natural gas specifications.

References:

1. GTE Interoperability Report, 2001. 

2. J. Wardzinski, M. M. Foss and F. Delano: Interstate natural gas - quality specifications & interchangeability. Center for Energy Economics, Houston, USA.