In spring of 2016 (maybe may) i was working for intel and flying on the corporate commuter jet which seats around 50 people from hillsboro, or into san jose, ca. this was a flight i'd taken many times before. it was a clear, sunny day, close to midday. we had begun descent, flying generally over tomales bay (i think). we were at perhaps 5000-10000ft (rough estimate). i was sitting on the right side of the plane, so looking out the window i could see to the s-sw. i was watching a several other planes (smaller ones, i thought) below us against the backdrop of hills around what i believe was point reyes, most of which were flying along a similar trajectory. the hills were very green at that time of year, so that provided a good contrast. as i was watching one particular other plane, very small and below us/to the sw flying in roughly the same direction, a highly reflective silver/chrome spherical object flew between our plane and the one below. it was headed on what seemed to be a se to nw trajectory (so roughly opposite relative to my plane). it appeared much closer than the other plane, making it seem maybe 10-20ft in diameter. it flew along a straight line at a speed which seemed at the time to be very fast, faster than our plane. it was in my view for maybe 2-3 seconds, long enough to think, 'what the heck is that? distance, size, and speed were very difficult to judge, of course, so this is just how it appeared to me. i didn't see any apparent means of propulsion' just a sphere. i asked a colleague if she had seen anything when we landed, but she had been working on her laptop, not looking outside. for the record, i hadn't had any alcohol or other substances and judging by the detail i could see of other planes my visibility was quite good. at the moment it happened i thought perhaps some kind of drone, but it looked much too large, too fast, too high and with no propellers and not shaped like any drones i've seen before or since. i've wondered since if it may have been a weather/science balloon or just a trick of light, but it looked perfectly smooth and reflective, with no seam or other features and it was a perfect sphere, which is unlike any weather balloon i've ever seen. plus who would launch a weather balloon that big in such a busy flight path? and as for being a trick of light, like a reflection from another plane or something, i just don't think so. i saw a spherical object, just as clearly as i could see anything else. this has been a strange aside i've mentioned a few times over the three years since when the subject of ufos comes up. i've googled it and saw a few mentions of reports that seemed similar, but it wasn't until today reading about the navy's updated policies for their pilots to report sightings that i decided to file my own report, for whatever it's worth. the washington post reported, 'in some cases, pilots' many of whom are engineers and academy graduates 'claimed to observe small spherical objects flying in formation. [...] these vehicles all had no air intake, no wind and no exhaust. i thought gosh, that's damn close to what i saw. maybe the pilots saw it, as well. at any rate, it's the only ufo i've ever seen. pretty bizarre.