I have some historical options data, and there are duplicates of some options, how to filter them

Question

I have some historical EOD options data for 2013, and there are duplicates listed for same strikes/expirations. I was told that by the provider that this is due to "special one-time cash payout" for the company as opposed to a normal dividend, and this is how it is accounted for. My questions are

1. Can anyone explain what "special cash payout" means?
2. How can I tell which is the real option price?

Example from 1/2/2013:

   Underlying UnderlyingPrice   Expiry Type Strike Last  Bid  Ask Volume OpenInterest  Mark   IV 
1:        WNR           28.94 20130119    C     30 0.85 1.05 1.10      7         1206 1.075 0.58 
2:        WNR           28.94 20130119    P     30 1.70 0.65 0.75      0          134 0.700 0.43 
3:        WNR           28.94 20130119    C     30 0.30 0.35 0.45    370          166 0.400 0.31 
4:        WNR           28.94 20130119    P     30 1.05 1.45 1.85      0            0 1.650 0.80

Answer 1

When the underlying asset is a stock making this special dividend to its shareholders, it will influence the option.

Special dividends is not that common, but usually happens in companies with extraordinarily success or under liquidation / sale of a division / splitting up. Look at Special Dividend on Wikipedia.

Answer 2

When a company distributes a special dividend or there is other corporate action, it affects the deliverable of the option contracts. Thus, the option is adjusted and becomes special.

For example, a standard option contract is on 100 shares of ABC. The company goes through a corporate action (including special dividends), and the deliverable now is 90 shares of the adjusted underlying share.

Typically, new options with standard properties are issued around the corporate action date. They may trade for a certain period together with old (non-standard) options with the same strike, expiration, callput.

Eventually, the non-standard options will be delisted and standard contracts will continue trading.

A provider should give you some sort of identifier to distinguish between the old (non-standard) option and newly listed option.