When citing computations performed with PETSc in a publication, plus run the application code with all the options you usually use and the option -citations optionalfilename This will generate a list of bibtex references appropriate for that computation. Otherwise please cite the following:
          @Misc{petsc-web-page,
            author = {Satish Balay and Mark~F. Adams and Jed Brown and Peter Brune
                      and Kris Buschelman and Victor Eijkhout and William~D. Gropp
                      and Dinesh Kaushik and Matthew~G. Knepley
                      and Lois Curfman McInnes and Karl Rupp and Barry~F. Smith
                      and Hong Zhang},
            title =  {{PETS}c {W}eb page},
            url =    {http://www.mcs.anl.gov/petsc},
            howpublished = {\url{http://www.mcs.anl.gov/petsc}},
            year = {2014}
          }

          @TechReport{petsc-user-ref,
            author = {Satish Balay and Mark~F. Adams and Jed Brown and Peter Brune
                      and Kris Buschelman and Victor Eijkhout and William~D. Gropp
                      and Dinesh Kaushik and Matthew~G. Knepley
                      and Lois Curfman McInnes and Karl Rupp and Barry~F. Smith
                      and Hong Zhang},
            title  = {{PETS}c Users Manual},
            institution = {Argonne National Laboratory},
            year   = 2013,
            number = {ANL-95/11 - Revision 3.4},
            url    = {http://www.mcs.anl.gov/petsc}
          }

          @InProceedings{petsc-efficient,
            Author = "Satish Balay and William D. Gropp and Lois Curfman McInnes and Barry F.  Smith",
            Title = "Efficient Management of Parallelism in Object Oriented Numerical Software Libraries",
            Booktitle = "Modern Software Tools in Scientific Computing",
            Editor = "E. Arge and A. M. Bruaset and H. P. Langtangen",
            Pages = "163--202",
            Publisher = "Birkh{\"{a}}user Press",
            Year = "1997"
          }