Call/Put Open interest difference on similar underlying

Question

High open interest for a given option contract is an indicator for interest in that option. For that reason I wanted to take a look at how the open interest of options on volatility have evolved in the last years. To do so, I took a look at VIX options and options on the VXX (ETN on the VIX, options exist since 2010). Plotting the results in a stacked bar chart:

The growth of total open interest has been identical on the two types of volatility options. But the relation between call and put open interest is very different. Considering the close relationship between the VIX index and the VXX ETN, this comes as a surprise to me. Does anyone have a possible explanation or idea why the call/put open interest ratio is so different between the two?

Answer 1

just like every ETF, it represents a sample and never tracks anything perfectly, it is worth reading the details, for instance at:

https://www.etf.com/VXXB

moreover the VXX is not even an ETF, but an exchange traded note, a debt instrument associated with a counterparty, hence a wholly different thing than the VIX index.

Answer 2

Does anyone have a possible explanation or idea why the call/put open interest ratio is so different between the two?

They have different underlyings. VXX tracks SPVXSTR. VIX options are options on VIX futures. My guess is option volumes on VIX lean toward calls because they're often used as a way to hedge risky assets; options on VXX are often used to play the rolldown hence more volume in put structures. At the very least, this is consistent with the trade recommendations I see from the sellside/brokers. HTH.