To cite package gstat in publications use:

Pebesma, E.J., 2004. Multivariable geostatistics in S: the gstat package. Computers & Geosciences, 30: 683-691.

Corresponding BibTeX entry:

  @Article{,
    title = {Multivariable geostatistics in S: the gstat package},
    author = {Edzer J. Pebesma},
    journal = {Computers & Geosciences},
    year = {2004},
    volume = {30},
    pages = {683-691},
  }