[50] Wandel et al. (1992) suggest that supply and demand on the logistics market should preferably match, but the findings from this paper indicate this is not the case for the green logistics market. As described earlier in this paper, the study involves five different gaps, all of which deal with the LSP-shipper interface. Three of these gaps are external (both LSPs' and shippers' views are included) and two are internal (either LSPs' or shippers' views are included), and interestingly the two internal gaps represent both the largest and the smallest gaps. Gap 2, where LSPs give their views on their own offers and their perception of demands, is the largest gap, whereas Gap 5, where shippers give their view on their own demands and the LSPs' offers, represents the smallest. Moreover, a comparison between the five different gaps shows that Gaps 1-3 are generally the largest ones.
For Gap 1, which focuses on LSPs' stated offers versus shippers' stated demands, the LSPs' stated offers have higher mean values for all green categories than do the shippers' stated demands. This makes Gap 1 a positive gap in accordance with the terminology of [31] Ling and Brooks (1998). If this is in fact the case, it is possible that service quality is too high, as suggested by [28] Large and König (2009), and that LSPs could use resources better elsewhere. Another possible explanation as to why the LSPs' supply of environmental services exceeds the demands of the shippers could be that the LSPs expect green demands to increase in the future and thus want to be prepared. Regardless of the reason, this study indicates that the LSPs over-achieve when it comes to their environmental offers.
For Gap 2, where LSPs are asked about their own green offers and their perception of shippers' green demands, the gaps are even larger than for Gap 1 ([31] Lings and Brooks, 1998). As previously mentioned, Gap 1 shows over-achievement and Gap 2 deepens the understanding indicating that LSPs seem to be aware of the fact that they over-achieve. Moreover, LSPs seem to think that they are further ahead of shippers. The fact that LSPs both seem to be aware of their over-achievement and perceive the gap in the interface as rather large, supports the suggestion that LSPs want to be prepared for future environmental demands. However, a discussion of the reason for the gaps is beyond the scope of this paper.
A closer look at Gap 3, which examines LSPs' stated offers vs the shippers' perception of those offers, reveals that shippers do not share the same perception of green supply as LSPs. For all green categories the shippers' responses result in lower mean values than those of the LSPs'. This could mean one of two things: first, it is possible that the LSPs offer more than the shippers are aware of; if this is the case, Gap 3 could show that the LSPs fail to communicate their environmental offers on the green logistics market. Second, Gap 3 could indicate that the shippers have different views and different levels of maturity when it comes to the green categories. Thus, although communication between the two actors might be clear, the shippers and the LSPs do not fully understand one another. Again, it is not possible to get a full explanation for Gap 3 from the survey used in this study.
Gap 4, which asks both LSPs and shippers for their views of demand in the interface between the two types of actors, the shippers' demands exceed the LSPs' perception of the demands. This is interesting, as this gap is the only one where the shippers have higher mean values than the LSPs, and it is thus the only negative gap ([31] Lings and Brooks, 1998) of the five studied. However, compared to Gap 3, the gaps are relatively small for most of the green categories. This could indicate that shippers are more successful in communicating their green demands than the LSPs are in communicating their green offers. On the other hand, it could also suggest that LSPs underestimate the shippers' green demands, and that shippers are in fact not good enough at communicating their demands.
The final gap studied is Gap 5, which shows the shippers' views on both green supply and green demand. The lack of gaps suggests that shippers are pleased with the offers from the LSPs since their demands are met. Interestingly, the shippers do not seem to see the big gaps between the green offers and green demands that the LSPs seem to perceive in Gaps 1 and 2. Thus, the shippers do not seem to perceive the possible over-achievement that the LSPs describe. As suggested earlier, one explanation for this could be that there is a lack in the communication between the LSPs and the shippers when it comes to environmental offers.
[51] Wolf and Seuring (2010) suggest that LSPs' green supply exceeds the shippers' green demands and, although this is a conclusion that is not related to the different green categories of this study, this suggestion supports the general findings presented in this paper.
Perceptions of the categories studied
This study suggests that there are several gaps on the green logistics market. However, the gaps identified can be the result of how the respondents' perceived the categories studied. For each of the gaps discussed above, it is possible that LSPs and shippers have different perceptions of the categories and therefore have different points of reference. It is also possible that respondents within the same actor group (LSP or shipper) have different perceptions of the green categories. The survey responses, and therefore the mean values too, are naturally dependent on these perceptions. The confidence intervals illustrated in the Appendix can provide some guidance in this matter as they indicate that the same actor group seems to share approximately the same understanding of the categories. Some very small tendencies towards variations (longer confidence intervals) is, however, notable in Gap 1, suggesting that LSPs have a more similar view of their stated offers, as compared to the shippers' view of their stated demands. In Gap 2 a similar small tendency can be identified, suggesting that LSPs have more similar views of their stated demands as compared to how they perceive the shippers' demands. Future research is needed to confirm if these tendencies actually exist, and to bring clarity as to why these differences may occur.