“…A detailed analysis of literature data for five ILs, namely [C 2 C 1 im][BF 4 ], [C 4 C 1 im][BF 4 ], [C 4 C 1 im][PF 6 ], [C 4 C 1 im][NTf 2 ], and [C 6 C 1 im][NTf 2 ], was presented as examples in order to show real difficulties and problems with consistency of speed of sound data sets. For [C 2 C 1 im][BF 4 ] among 12 papers, − published up to 2014, in 11 there are identical data sets, in some cases differing in decimal places (i.e., one or two); only data reported by Sharma et al are different; however, they did not compare these results with their own data reported in other papers. Therefore, finally, the analysis of consistency of speed of sound data was presented for four ILs, i.e., [C 6 C 1 im][NTf 2 ] ,,,, as a substance recommended by IUPAC, [C 4 C 1 im][BF 4 ], [C 4 C 1 im][PF 6 ], as well as for [C 4 C 1 im][NTf 2 ]. ,,,,,,,, The purity of these ILs is compared in Table .…”