<center> https://image.ibb.co/kKwGNw/Screenshot_10.png </center>
The ICO EOS rules are different from other ICOs distribution of tokens takes place in 351 24-hour periods in each 2000000 EOS tokens are distributed among participants(except period 0 where 200M EOS tokens were sent).
<center> https://image.ibb.co/cgBSUb/Screenshot_9.png </center>

Usuall price in each ICO perios is almost the same as on the exchanges, but in period 164 ico the price was 0.7 $ higher than  on exchanges 4,45$(ico price) compared to 3.74$(exchange price). 
I see 2 reasons why that has happend. 
Yesterday @dan announced EOS DAWN 2.0 release - [dan post](https://steemit.com/eos/@eosio/eos-io-dawn-2-0-released-and-development-update#@dan/re-muad-dib-re-eosio-eos-io-dawn-2-0-released-and-development-update-20171204t204650566z)
and also yesterday the game based on ethereum blockchain called cryptokitties started [about kitties](https://steemit.com/ethereum/@whd/how-kitties-destroyed-ethereum-blockchain-in-just-one-day-17k-transactions-pending) and this game has caused ethereum network congestion (16711 pending transactions while writing post).
Probably these two reasons caused significant price differences. The only conclusion that can be drawn is - do not use ethereum network at moments of heavy load