I have a Canadian dollar, no FTF Visa credit card issued by Chase Canada (it's an Amazon.ca branded card). I've been paying with it while living in Australia half time. The forex cost of using it for expenses here has compared favourably with any method for bringing lump sums from Canada, even without considering the 1% dividend Chase pays on all purchases.

I have routinely monitored the actual exchange rate charged on each Australian dollar transaction and it has always been equal, or very close, to the daily rates published here by Visa Inc. I think any differences are due to wide swings in the rate within a day.

What has struck me recently is that the spread between Visa's rates and those reported by OANDA or XE suddenly widened on Dec 5 2015. For the 2.5 years I've been using the card, the spread has always been about half a percentage point. Suddenly it has jumped to about 1.25 percentage points for my last 26 transactions. I've sent a note asking Visa about it.

In the meantime I'm wondering if anyone can shed some light on the relationship between Visa's rates and the interbank rates, for this or any other currency pairs?