Context : To investigate the properties of the 21-cm radio-lines of galactic neutral hydrogen , the profiles of “ The Leiden/Argentine/Bonn ( LAB ) Survey of Galactic H i ” are decomposed into Gaussian components .

Aims : The width distribution of the obtained components is analysed and compared with similar studies by other authors .

Methods : The study is based on an automatic profile decomposition algorithm .
As the Gaussians obtained for the complex H i profiles near the galactic plane can not be directly interpreted in terms of the properties of gas clouds , we mainly study the selected simplest profiles in a limited velocity range .
The selection criteria are described and their influence on the results is discussed .

Results : Considering only the simplest H i profiles , we demonstrate that for Gaussians with relatively small LSR velocities ( -9 \leq V _ { \mathrm { C } } \leq 4 ~ { } \mathrm { km s } ^ { -1 } ) it is possible to distinguish three or four groups of preferred line-widths .
The mean widths of these groups are \mathrm { FWHM } = 3.9 \pm 0.6 , 11.8 \pm 0.5 , 24.1 \pm 0.6 , and 42 \pm 5 ~ { } \mathrm { km s } ^ { -1 } .
Verschuur previously proposed similar line-width regimes , but with somewhat larger widths .
He used a human-assisted decomposition for a nearly 50 times smaller database and we discuss systematic differences in analysis and results .

Conclusions : The line-widths of about 3.9 and 24.1 ~ { } \mathrm { km s } ^ { -1 } are well understood in the framework of traditional models of the two-phase interstellar medium .
The components with the widths around 11.8 ~ { } \mathrm { km s } ^ { -1 } indicate that a considerable fraction ( up to about 40 % ) of the H i gas is thermally unstable .
The reality and the origin of the broad lines with the widths of about 42 ~ { } \mathrm { km s } ^ { -1 } is more obscure .
These , however , contain only about 4 % of the total observed column densities .