Tullow Oil's shares slumped on Tuesday as Credit Suisse reiterated a 'hold' rating for the stock and cut its target price from 1150p to 1050p a day ahead of the firm's trading update.The broker noted that oil and gas producer has been a relative underperformer with some high profit wells delivering disappointing results."Tullow offers exciting exploration, with an experienced management team that has demonstrated its ability to deliver success in frontier regions," Credit Suisse said on Tuesday. "However we remain concerned that, even after making an exception to our methodology to incorporate considerable value for entire geological basins, the valuation looks rather stretched."The share price has been volatile around significant well results, which creates challenges when assessing value. While management considers the volatility frustrating, Credit Suisse views it as an opportunity to take profits following success. Tullow is due to reveal test results from its flagship wells in Kenya, French Guiana, Mauritania and Norway by the end of the year.Wednesday July 3rdINTERIM EX-DIVIDEND DATECareTech Holding, Character Group, Chrysalis VCT, Driver Group, Dunedin Smaller Companies Inv Trust, ITE Group, Octopus Titan VCT 3, Paragon Group Of CompaniesQUARTERLY EX-DIVIDEND DATEBritish Land Co, Investors Capital Trust 'A' Shares, Torchmark Corp.INTERNATIONAL ECONOMIC ANNOUNCEMENTSCrude Oil Inventories (US) (13:30)ISM Non-Manufacturing (US) (15:00)ISM Services (US) (15:00)MBA Mortgage Applications (US) (13:30)PMI Composite (EU) (09:00)PMI Composite (GER) (08:55)PMI Services (EU) (09:30)PMI Services (GER) (08:55)FINALSBegbies Traynor GroupSPECIAL DIVIDEND PAYMENT DATESpirax-Sarco EngineeringSPECIAL EX-DIVIDEND PAYMENT DATEElectronic Data ProcessingAGMSBahamas Petroleum Co, Clean Air Power Ltd, Home Retail Group, Oxford Technology 2 VCT, Oxford Technology 3 VCT, Oxford Technology 4 VCT, Oxford Technology VCT, Zoltav Resources IncTRADING ANNOUNCEMENTSTullow OilUK ECONOMIC ANNOUNCEMENTSBRC Shop Price Index (00:01)Halifax House Price Index (09:30)Official Reserves (09:30)PMI Composite (09:30)PMI Services (09:30)FINAL DIVIDEND PAYMENT DATEBlackRock Smaller Companies Trust, Staffline GroupFINAL EX-DIVIDEND DATEAnpario, Babcock International Group, Bisichi Mining, Brightside Group, Burberry Group, Chamberlin, Cranswick, De La Rue, Dee Valley Group, Dee Valley Group (Non-Voting), E2V Technologies, Halfords Group, Helical Bar, Homeserve, Martin Currie Pacific Trust, MS International, Northern 2 VCT, Northern 3 VCT, Plastics Capital, Printing.com, ProVen Growth & Income VCT, Rensburg AIM VCT, Sepura, Shanks Group, TalkTalk Telecom Group , TrifastRD