The shares of BHP and BBL that trade on the NYSE are ADR’s which track their home-market shares in Sydney and London, respectively. So the real question is why there is a disparity between the prices of the home-market shares?
Differences in trading liquidity (of the home-market shares, not the ADR’s) could explain some disparity in the prices of BHP and BBL, but not a spread as large as 16%.
Could the dividends for BBL be any less secure?
No. Shareholders of the two parent companies have identical rights with respect to receiving a dividend—the only distinction is in the form of payment and the tax withholding, as mentioned in #msg-41930863.
I am looking for other ideas to explain this discrepancy.
The best explanation, IMO, is the quotation at the bottom of this message :- )
“The efficient-market hypothesis may be the foremost piece of B.S. ever promulgated in any area of human knowledge!”