Compel Technic

Hey guys. Forum newbie here. I'm coming to you guys to find the answer to a question that has been bothering me. I've been getting into volatility index ETF based options lately, and have come across something weird that I need to figure out. It appears that for some ETF's, forsome expiry months of those ETF's, there are two unique call and two unique put options at each strike price. As an example, here are links to the January expiration options for VXX: http://www.nasdaq.com/symbol/vxx/option-chain?money=all&dateindex=4 http://finance.yahoo.com/q/op?s=VXX&m=2014-01 Looking at the January 2014 options, we have both of these options symbols, with their associated trading values from yahoo finance as of 8/14/2013: VXX140118C00009000 0.10 VXX1140118C00009000 5.65 (*) I would like what the difference between these two options actually is, that makes them worth different prices on the market. I have tried looking through options chain data on yahoo, nasdaq, etc. to find this information, but to no avail. I've tried googling this information, but have not been able to find any info. that would help:angry:. So here I come to you to ask- what gives? Why are there two symbols different, and why do they both exist only some of the time? If it helps for identification purposes, the second option(with the *) has an extra 1 inserted into the symbol, and the other option has a symbol that matches the usual format. So far, all of my research has led to nothing- so I need your help. I'm much obliged! P.S. It may interest you that I'm working on a python program to estimate the value of volatility ETF options at expiry. The program scrapes options value data, as well as the historical prices of the underlying ETF, in order to generate a probability distribution function of the value of each option at expiry, assuming that the underlying ETF has similar price movement behavior as it has shown in the past. See the program on github: https://github.com/CompelTechnic/QuickieStockAndOptionsScraper