What are the actual risks and likelihood of stds when having sexual intercourse with a condom but not using any protection for oral sex (69)?  Both partners have no symptoms of anything and always use condoms otherwise.  

There are two parts to these questions.  I'll try to provide some information.  Overall, the risk for any single episode of sexual contact with a new partner the risk is low- most people, including commercial sex workers do not have STIs and there are no STIs that are transmitted the majority of the time with a single encounter.  Persons with multiple new casual partners are somewhat more likely to have an asymptomatic infection than persons who have not had other recent partners.  Genital-genital contact is far more likely to result in infection because genital infections are more common than oral infections.  (LMK if you wish to include penetrative rectal sex in this question).  Oral infections are less common for all STIs and transmission from the infected mouth to a partner's genitals is a less biologically efficient process than genital-genital contact.  Condoms offer a further greater than 95% reduction in risk for STI, including HIV acquistion if the condom is worn throughout the encounter and does not break (which is relatively uncommon).---

Let's set intercourse aside and focus on exchanging of oral sex with a new partner.  What is the likelihood of getting an infection (and which infections are possible?) if the new partner shows no signs of infection? 

Persons who have STIs can be asymptomatic.  Most pharyngeal gonorrhea is asymptomatic.  The major concerns related to receipt of oral sex are acquiring gonorrhea.  Persons who do not have herpes type 1 (60% of the population have HSV-1 and most do not know it) have a very small chance of getting genital herpes due to HSV-1.  EWH---