Which spells have to beat the OR? All of them or only those whose decriptions say so?

If the former is the case, there are some pretty weird cases. You can more easilylevitate a 200kg anvil on your opponents than a grenade. If you want to levitate your commlink you better put it into a jute bag (without RFIDs).

According to RAW it is even intended that a rock is more flammable than gasoline if you use the ignite spell.

All of them, except physical attack spells like Lightning or Firebolt.

So to ignite a puddle of Gas, you're better off throwing a fireball at it than trying to Ignite it.

This is a valid concern. It would make most spells useless.

Help me out, how was this solved in earlier editions?

Physical Illusions are the only group of spells that all need to go against OR to work. Otherwise per specific spell description.

Petroleum is a naturally occurring chemical, so it could be OR 1.

When choosing between the interpretation that makes a lot of things pointless, and one that makes most things reasonable, you probably want to go with the one that doesn't make everything useless.

Edit: Direct Combat Spells cast against Non Living Targets also go against OR as a group.

This is where I come in with my spur of the moment House Rule saying that any spell that specifically states that it effects technology gets a certain number of automatic successes towards OR (my original thought was 1, but last night I came up with Force/3 round up).

In the back of Street Magic is table telling, among other things, what kind of test is used to cast each spell.
May be outdated now, but still useful.

According to it Levitate is only success test, no OR.

I know that table but unfortunately
There is no mention that there are exceptions to this rule, except for indirect combat spells, AFAIK.

Check Sr4 p. 195 , "Spells that aff ect non-living targets are not opposed,
but may have a threshold for the spell to succeed (see Object
Resistance, p. 174)." which has that pesky word "may"

You can also look at the general spell category and group descriptions which include telling us when OR is used for the group, and in specific spell descriptions which spell out when OR is used for specific spells.

If OR is always used in all cases, why do particular groups and specific spells need to have an additional reference to OR rather then there being a general formula for all Threshold/Resistance tests to be X + Y + OR ?

If there seems to be a discrepancy between different sections and you end up needing to choose between one being wrong and the other right, and there isn't other clarifying evidence to settle it, you have several strategies for choosing. In this case the preponderance, category and individual spell description cases citing OR, and the general easier spell casting functional game mechanic, seem to indicate that OR isn't universally added to all spells resistance tests.

That pesky word was one of the reasons I posted the topic. It contradicts the line on p. 174.

You're going to have to choose which way you want to do it. It's your choice which way you want to do it. You have all the evidence, you decide.

Guess this is again something which should have been adressed in the errata, before changing fundamental aspects of magic.

A thought ocurred to me with this thread. I can't recall and I'm at work so I have no acces to the books, do the Ram/Wreck/Demolish spells specifically mention OR? With that 'may' word in there, could it be implied that that collection of spells wouldn't have to worry about OR since they are custom tailored to specific objects?

I believe Ram/Wreck/Demolish does call for OR in the spell description.

According to my handy Street Magic PDF on the Spell Table on p.187, all of those are explicitly Success Tests with an Object Resistance Threshold.
The text on SM p.165 doesn't say specifically, but the BBB on p.196 is pretty clear on that for Direct Combat Spells.

Ram / Wreck / Demolish are all Direct Combat spells and so subject to the OR threshold to affect the target. Spells like Levitate and Fling have no reference to OR which I thought I'd mention because someone earlier commented that it was now easier to hurl a 200kg boulder than it was to move a 200g commlink. That's incorrect.

EDIT: TRIPLE-NINJA!

It is only incorrect if you decide that the line on p. 195 of the BBB is more important than the one on p. 174.

Triple Ninja?

True. It would have been nice if that were cleared up in the new edition. It's generally accepted that the more specific text on pg. 195 of SR4 BBB takes precedence. Unfortunately SR4A has introduced a second and similar contradiction which is whether or not objects get a resistance roll against Direct Combat spells.

I hope the devs are reading all this and have a little time to make some adjustments before it goes to press.

Ninja'd = Someone sneaking in a post while which says the same as yours while you're still typing. Triple-Ninja'd = THREE people did it. Note to self - be less wordy.

K.

It took you 29+ minutes? I made my "ninja" at 4:07. The next two are at 4:15 and yours at 4:36...

I have, of course, ninja'd people by 4 hours before. Only because I made a short post that was a link to the answer and NO ONE BOTHERED CLICKING IT. Annoyed me a lot, as that particular question got asked about 8 times that week and the answer takes about 15 minutes to type out.

I'm multitasking.

Badly.

Ahhh.