Chloronaphthalene (CN) congeners and homologue groups have been quantified in up to three batches of several types of technical CN formulations of the Halowax series (Halowax 1031, 1000, 1001, 1013, 1014 and 1099), to elucidate possible batch-to-batch compositional variations. Using isotope dilution and HRGC/HRMS a relatively large variation in CN congeners and homologues composition among the batches of particular types of the Halowax formulations could be noted, and also when compared to the composition declared by the manufacturer. Depending on the type of the Halowax formulation and its batch in total up to 54 peaks from chloronaphthalenes (Agilent Ultra 2 liquid phase), which represented 70 of 75 CN congeners theoretically possible, could be found in these mixtures. These congeners represented all CN homologue groups from mono- to octaCN but some co-eluted. A co-eluting congeners were such as: 1,4-/1,6- (nos. 5/7), 1,5-/2,7- (nos. 6/12), 2,6-1,7- (nos. 11/8) of diCNs; 1,3,6-/1,3,5- (nos. 20/19), 1,3,7-/1,4,6- (nos. 23/24), 1,6,7-/2,3,6- (nos. 25/26) of triCNs; 1,2,5,7-/1,2,4,6-/1,2,4,7- (nos. 37/33/34), 1,3,6,8-/1,2,5,6- (nos. 45/36), 1,2,3,5-/1,3,5,8- (nos. 28/43), 1,2,3,4-/ 1,2,3,7- (nos. 27/30), 1,2,5,8-/1,2,6,8- (nos. 38/40) of tetraCNs; 1,2,3,5,7-/1,2,4,6,7- (nos. 52/60), 1,2,3,5,8-/1,2,3,6,8- (nos. 53/55) of pentaCNs; 1,2,3,4,6,7-/1,2,3,5,6,7- (nos. 66/67), 1,2,3,4,5,7-/1,2,3,5,6,8- (64/68) and 1,2,4,5,6,8-/1,2,4,5,7,8- (nos. 71/72) of hexaCNs. Absent in the Halowaxes were CN congeners such as 1,3,8-triCN (no. 22) (<0.0002 mg/g), 1,3,6,7-tetraCN (no. 44), 1,2,3,6-TetraCN (no. 29), 1,2,3,6,7-pentaCN (no. 54) and 1,2,3,6,7,8-hexaCN (no. 70) (<0.0005 mg/g).